Susan Walsh/AP Photo

By MICHAEL FALCONE ( @michaelpfalcone )

NOTABLES

• MOMENTUM SHIFT? The Washington Post's Philip Rucker and Ed O'Keefe report: "Gun-control measures that seemed destined to become law after the school shootings in Newtown, Conn., are in jeopardy amid a fierce lobbying campaign by firearms advocates. Despite months of negotiations, key senators have been unable to find a workable plan for near-universal background checks on gun purchases - an idea that polls show nine in 10 Americans support. Another provision that garnered bipartisan support - making gun trafficking a federal crime - could be gutted if Republican lawmakers accept new language being circulated by the National Rifle Association." http://wapo.st/YOYpx8

• HAPPENING TODAY: "Asa Hutchinson, former United States Representative, former United States Attorney, and former Under Secretary for Border & Transportation Security at the U.S. Department of Homeland Security, will be announcing the findings and recommendations of the National Rifle Association's National School Shield Program." 11:00 a.m., The National Press Club

• TUNE IN: Tonight, ABC's DIANE SAWYER interviews a teacher who survived the Newtown shootings. Kaitlin Roig tells Diane about a nonprofit website she is launching called "Classes for Classes," which will focus on teaching compassion to young children. (h/t ABC's Don Ennis)

THE ROUNDTABLE

ABC'S JIM AVILA: The Senate Gang of 8 led by Arizona Sen. John McCain and New York Sen. Charles Schumer is poised to introduce a comprehensive immigration bill as soon as next Monday, April 8, according to sources briefed on the timetable. As Schumer, a Democrat, said over the weekend the big moving parts of a bill have been agreed to in principle and details are being worked out this week. The current timetable according to Hill sources is the Senate introduces the bill, holds hearings and votes by July. The House version will likely be introduced the week of April 14. The House Gang of 8 is still waiting to hear if leadership will endorse its bill. Sources close to the House members working on its version tell ABC News its version is likely to be "a couple inches to the right of the Senate's" and voted upon in the fall. A realistic timetable for a bill emerging from the House and Senate conference would then be Thanksgiving. That may seem like a long time for those not versed in the ways of Capitol Hill. But that is actually lightning speed. It's quite unusual for legislation to be introduced and passed in the same calendar year. http://abcn.ws/Z43NIK

ABC's CHRIS GOOD: Mark Sanford will try his luck again tonight in South Carolina's primary runoff, in which he'll face former Charleston County Council member Curtis Bostic. The winner will become the Republican nominee for the seat, facing Elizabeth Colbert Busch in the general election. This time, it'll get a bit easier to judge the most interesting question of this race: Have the voters "forgiven" Sanford? The former governor's House run has tested the limits of personal redemption in the public sphere, but in the primary's first round, 15 other GOP opponents made it tough to say whether Sanford's 37 percent was good or bad. He's expected to win tonight, and win handily, but if he doesn't best Bostic by a wide margin, it could cast some doubt over the political comeback of the century.

ABC's SHUSHANNAH WALSHE: Sen. Bob Casey, D-Pa.'s expression of support for same sex marriage yesterday made the group of Democratic senators who still oppose gay marriage in some way a that much smaller. Casey said letters from couples who wanted to get married directly affected his decision - mail the remaining eight senators must be receiving as well. The question for Heidi Heitkamp of North Dakota, Joe Manchin of West Virginia, Mary Landrieu of Louisiana, Joe Donnelly of Indiana, Mark Pryor of Arkansas, Tom Carper of Delaware, Bill Nelson of Florida, and Tim Johnson of South Dakota must be this as they read their own letters from couples: Who doesn't want to be the last to flip?

ABC's DEVIN DWYER: After four years as spiritual adviser to the leader of the free world, Joshua DuBois says the biggest test of President Obama's personal faith came late in his first term, when a gunman massacred 20 children and 6 others at Sandy Hook Elementary School in Newtown, Conn., in December. "Seeing the strength of those families face to face in those quiet moments, seeing [not only] the depth of their pain, but also the height of their resilience was something that I'll never forget," DuBois told me in a recent interview. "I will also never forget what it took for the president to be a comforter over and over again to folks that had experienced unimaginable loss," he said. "He poured out his heart both in his public speech and behind the scenes in his private conversations." Until he stepped down earlier this year, DuBois was the only ordained member of Obama's inner circle, a role that won him the informal title of "pastor in chief" and "Obama's man of God." Later this year, DuBois plans publish a book for leaders based on the devotionals he shared with Obama; it will be called "The President's Devotionals." http://abcn.ws/11gmu0D

WHAT WE'RE WATCHING

OBAMA SPIRITUAL ADVISER SEES VIBRANT FAITH IN 'COMFORTER IN CHIEF.' Joshua DuBois is not your ordinary pastor. For the past four years, the 30-year-old Pentecostal minister was the spiritual adviser to President Obama, praying with him in the Oval Office and leading the administration's outreach to faith-based groups. "He's a deeply faithful president and didn't need a whole bunch of help cultivating that faith," DuBois said of Obama in an interview with ABC's DEVIN DWYER on his term as director of the White House Office of Faith-Based and Neighborhood Partnerships. "I would say that he has a daily Christian walk, in terms of his reading a devotional and spending time meditation-meditating on scripture each day." While some critics have questioned the depth of Obama's religious convictions, DuBois described a president who sees spiritual practice as extending beyond the confines of scripture and traditional religious rituals. Obama "considers spending time with his daughters and tucking them in at night… being a mentor and friend to so many and comforting the nation in times of need" as everyday manifestations of his Christian faith, he said. WATCH: http://yhoo.it/101VIHW

BUZZ

WHITE HOUSE ON THE BRAIN. This morning, President Obama will unveil a major initiative to map the human brain, senior advisor Dan Pfeiffer tells ABC's ANN COMPTON. This is a long term project that would not get off the ground, or even define itself, until 2014. The scientists involved sound psyched, telling the NY Times: "The goal here is a whole new playing field, whole new ways of thinking," Dr. William Newsome of Stanford said. "We are really out to catalyze a paradigm shift." The White House compares this to the Human Genome Project. The federal government will invest $100 million in seed money while universities will kick in additional funds.

FLASHBACK: President Obama alluded to the initiative in his State of the Union address: "If we want to make the best products, we also have to invest in the best ideas. Every dollar we invested to map the human genome returned $140 to our economy. Today, our scientists are mapping the human brain to unlock the answers to Alzheimer's; developing drugs to regenerate damaged organs; devising new material to make batteries ten times more powerful. Now is not the time to gut these job-creating investments in science and innovation. Now is the time to reach a level of research and development not seen since the height of the Space Race. We need to make that investment."

CASEY IS LATEST SENATE DEM TO EMBRACE GAY MARRIAGE. Another Senate Democrat, Sen. Bob Casey of Pennsylvania, came out yesterday in support of same-sex marriage, ABC's SUNLEN MILLER notes. "After much deliberation and after reviewing the legal, public policy, and civil rights questions presented, I support marriage equality for same-sex couples and believe that DOMA should be repealed," Casey said in a statement. The senator says letters he received from LGBT couples challenged him directly and "had a substantial impact on my position on this issue." "If two people of the same sex fall in love and want to marry, why would our government stand in their way? At a time when many Americans lament a lack of commitment in our society between married men and women, why would we want less commitment and fewer strong marriages? If two people of the same sex want to raise children, why would our government prevent them from doing so, especially when so many children have only one parent, or none at all?" Casey asked in his statement. http://abcn.ws/10tfpWE

AND THEN THERE WERE EIGHT… Casey's flip on the issue marks the seventh Senate Democrat in a week to reverse course and embrace same-sex marriage. There are only eight Senate Democrats left who continue to oppose marriage equality. Those eight senators are Heidi Heitkamp of North Dakota, Joe Manchin of West Virginia, Mary Landrieu of Louisiana, Joe Donnelly of Indiana, Mark Pryor of Arkansas, Tom Carper of Delaware, Bill Nelson of Florida and Tim Johnson of South Dakota.

NEW LAW SPURS CONTROVERSY OVER GENETICALLY MODIFIED CROPS. An uproar has erupted on social media platforms in the days following President Obama's signing into law legislation opponents are deriding as the Monsanto Protection Act - but groups disagree about what the real consequences of the bill will be, ABC's SARAH PARNASS reports. The derogatory name for the bill refers to the biotech company, Monsanto, which opponents say lucked out with the measure's passage. Critics see it as a win for peddlers of genetically-modified foods and a danger to farmers and consumers alike. It passed as part of the continuing resolution whisked through Congress earlier this month to avoid a government shutdown slated for March 27. Obama signed that bill on Tuesday, while many in Washington were preoccupied with the debate over same-sex marriage. The section of the CR that groups are objecting to - section 735 - dealt with how questionable crops can be regulated. In the event that a seed is approved by the USDA but that approval is challenged by a court ruling, the seed can still be used and sold until the USDA says otherwise, according to that new law. It does not mention genetically modified crops by name, and it does not stop the USDA from taking those crops off the market in the future. http://abcn.ws/XF9qlt

IN THE NOTE'S INBOX

- SENATE SUPER PAC BEEFS UP STAFF. Today, the pro-Democratic Senate Majority PAC announced the hires of Karyn Brockman as Finance Director and Ty Matsdorf as Campaigns and Communications Director for the 2014 cycle. According to a release from the group, "Prior to joining Senate Majority PAC, Brockman has raised money for candidates, elected officials and organizations on local, state and federal levels from the Midwest, to Connecticut, to Texas. … She most recently served as Senator Chris Murphy's finance director where she raised over $10 million against the largest self-funder in the country. … Matsdorf will help develop and execute the campaign strategy for the individual senate races where Senate Majority PAC is involved. He will also oversee the earned communications and research operation for the organization. 'Ty's hyper-aggressive political nature will be a seamless addition to Senate Majority PAC,' said Rebecca Lambe, co-chair of Senate Majority PAC."

-MOVE ON PRESSURES DEMOCRATIC SENATORS ON GAY MARRIAGE. "MoveOn.org members from Arkansas, Florida, Indiana, West Virginia, South Dakota, North Dakota, Louisiana and Delaware are leading campaigns to urge their Senator not to be the last Democrat to come out in support of marriage equality. Only eight Democratic Senators have yet to support the freedom to marry for all couples.," according to an announcement from the group. "Yesterday, Pennsylvania Senator Bob Casey announced his support for marriage equality after more than 12,000 MoveOn.org members signed a petition to him." Petitions for the remaining eight holdouts: http://bit.ly/last8dems

WHO'S TWEETING?

@adamslily: RTD: @timkaine's first Senate bill seeks to help vets get jobs http://www.timesdispatch.com/news/state-regional/government-politics/kaine-s-first-senate-bill-seeks-to-help-vets-get/article_d2e1d195-9045-5fae-a098-399e0406c57c.html …

@maggiepolitico: Josh Margolin with a hell of a scoop this morning http://nyp.st/Xnv0eZ

@AlexPappas: NRA's Chris Cox calls Democratic bill mandating gun owners to get liability insurance "ridiculous on its face." http://dailycaller.com/2013/04/02/democrats-propose-10000-fine-for-gun-owners-who-dont-have-insurance/#ixzz2PJ2pzvU0 …

@tackettdc: SCOOP Dr Melgen discusses Menendez relationship "like brothers" via @BloombergNow http://bloom.bg/XmTHsf

@ethanklapper: . @samsteinhp and @aterkel find 100 sequestration cuts nationwide http://huff.to/10rOImX