By MICHAEL FALCONE

NOTABLES

• TED CRUZ ANNOUNCES 2016 PRESIDENTIAL BID WITH A TWEET: Texas Senator Ted Cruz officially announced his 2016 presidential campaign on Twitter just after midnight, posting a video saying it will require a "new generation" to lead the country, ABC's ARLETTE SAENZ reports. "It's a time for truth, a time to rise to the challenge, just as Americans have always done. I believe in America and her people and I believe we can stand up and restore our promise," the Republican senator says in the video. "It's going to take a new generation of courageous conservatives to help make America great again and I'm ready to stand with you to lead the fight." http://abcn.ws/1BnaCbo OFFICIAL WEBSITE: http://www.tedcruz.org/

• FACT: Today will be Ted Cruz's 810th day as a U.S. Senator. Barack Obama announced for President on his 768th day as a Senator, according to ABC's CHRIS DONOVAN.

• HOW CRUZ IS PRACTICING TO BE A PRESIDENTIAL CANDIDATE: An Associated Press photographer captured a series of shots of a would-be First Family in training on Sunday. They show Cruz during a walk-through at Virginia's Liberty University, a Christian college in Lynchburg, Virginia, where he deliver a speech this morning. In some of the photos, Cruz walks hand-in-hand with his wife, Heidi, and the couple's two daughters - apparently practicing everything from their wave to a kiss. http://abcn.ws/1COLtNV ABC's JONATHAN KARL on Cruz's big day: http://abcn.ws/1ECejvX

• WHO IS TED CRUZ? Cruz rose to political stardom in 2012 as a Tea Party candidate who secured the Republican nomination in the Texas Senate primary against then Lt. Gov. David Dewhurst, the establishment-backed candidate. In November of that year, Cruz won the Senate seat and is currently serving in his third year in the Senate. He has been an outspoken critic of President Obama's immigration and healthcare plans. Cruz, a Cuban-American, was born in Calgary, Canada to an American mother and a father who fled Cuba in the 1950's. Cruz held dual U.S. and Canadian citizenship until 2014 when he formally renounced his Canadian citizenship. Cruz received his undergraduate degree from Princeton University and graduated magna cum laude from Harvard Law School. From 2003 to 2008, he served as solicitor general in Texas. http://abcn.ws/1CJuzyw

ANALYSIS

ABC's RICK KLEIN: He hasn't gotten ahead by following the recommended practices of his peers, so why start now? Sen. Ted Cruz is taking advantage of a slow formal start to 2016 - along with a message-driving Obamacare anniversary - to become the first major candidate to formally declare for president this cycle. He doesn't enter as a favorite, though he does figure to be a factor - a big one, too. His first-in status gives him a jump in driving the ideological debate, carrying a message of disruption and action, not merely conservative rhetoric. This, of course, is the space Cruz thrives in, even if he's seldom made friends among elected leaders in his own party along the way. Cruz won't make too many frontrunners' lists at this stage. But his route to the nomination was never going to flow down from the top, anyway.

THE BUZZ

with ABC's VERONICA STRACQUALURSI

HEAD OF HOUSE HOMELAND SECURITY COMMITTEE DISTURBED BY EVENTS IN YEMEN. Rep. Michael McCaul, R-Texas, the chair of the House Homeland Security Committee, said Sunday that he was alarmed by the chaos that has engulfed Yemen, which has led to the withdrawal of U.S. special operations forces from the war-torn country, ABC's BENJAMIN BELL reports. The Texas congressman also cited the blurring of lines between the various Islamist extremist groups operating in the country as a threat. "I think these developments in Yemen greatly disturb me, because of the - their potential to attack the United States," McCaul told ABC News' Martha Raddatz on "This Week." Yemen, which is engulfed in a civil war, endured a string of attacks across its capital this week that left over 130 people dead, including at two Shiite mosques. http://abcn.ws/1MXCsn3

SOME SERVICE MEMBERS ON PURPORTED ISIS 'HIT LIST' UNFAZED BY THREAT. Several of the military service members whose personal information appears on a purported ISIS "hit list" said Sunday they are unfazed by the online threat, as military officials continued the process of notifying individuals named on the list. The personal information of 100 service members was posted on a website by a previously unknown group calling itself the "Islamic State Hacking Division" that urged "lone wolf" sympathizers to kill those named on the list, according to ABC's LUIS MARTINEZ. ABC News is not identifying the three service members who provided reactions to their personal information appearing on the list. http://abcn.ws/1GI9i7t

5 STORIES YOU'LL CARE ABOUT IN POLITICS THIS WEEK: ABC's SHUSHANNAH WALSHE highlights some of the stories your ABC News political team is tracking in the week ahead. http://abcn.ws/1xOaTnb The "This Week" roundtable on Sen. Ted Cruz announcing his 2016 run and Rep. Aaron Schock's resignation. WATCH: http://abcn.ws/1MXq5Hv

INSTAGRAM PHOTOGRAPHERS DESCEND ON THE WHITE HOUSE: HERE ARE OUR FAVORITES. More than 1,500 amateur and professional photographers applied but only about two dozen were selected by the White House to participate in a day of shooting on its grounds. It was all part of the White House's participation in a "Worldwide InstaMeet," a social media event hosted by Instagram a few times each year where people meet in specific places to "connect, take photos together and inspire one another," the photo-sharing company says. This was not the only time the administration had done an Instagram event: It once gave special access to its gardens and kitchen for a smaller domestic InstaMeet in 2013. Similarly it was used by the National Park Service when the Washington Monument was reopened and by the National Zoo to introduce its baby panda, Bao Bao. But this year was a first for participation in a world-scale meet, ABC's MATTHEW LAROTONDA writes. Here are some of our favorites from the shoot, but more can be found by following the "#WHInstaMeet" hashtag on Twitter or Instagram. http://abcn.ws/1FmyDGN

WHO'S TWEETING?

@HotlineScott: Cruz spent the months before his candidacy showcasing the field's most conservative views http://www.nationaljournal.com/2016-elections/how-ted-cruz-will-pull-the-gop-presidential-primary-right-20150322 …

@bethreinhard: Conservative warrior Ted Cruz jumps into 2016 race first, @hookjan reports on why and what it means http://on.wsj.com/19d4L1A via @WSJ

@KilloughCNN: Ted Cruz also released a different video in Spanish, one where someone else is narrating https://youtu.be/oB3smCq7Mjo

@TexasTribune: . @tedcruz takes his own path to nomination | @TexasTribAbby http://trib.it/1Bn7Hj8 #tx2016 #POTUS

@jeneps: Not a particularly flattering image of Clinton in Benghazi emails. "Did we survive the day?" She asked aide. http://mobile.nytimes.com/2015/03/23/us/politics/in-clinton-emails-on-benghazi-a-rare-glimpse-at-her-concerns.html …