Sen. Elizabeth Warren, meanwhile, has emerged as a leading contender -- if not the favorite -- for the Democratic nomination. Plans and selfies have gotten her to this point, with a slow-but-steady rise that's made her the central figure in the primary race at the moment.
With that comes new scrutiny that will gather around Warren this weekend in Iowa, where the major candidates are gathering for a series of events starting on Friday. Policy scrutiny of Warren is now coming from Stephen Colbert and some of her Democratic rivals, who are taking note of her non-answer when it comes to raising taxes on the middle class.
That scrutiny will stretch to her home state of Massachusetts, where a former student, Rep. Joseph Kennedy III, will announce a primary challenge on Saturday against Sen. Ed Markey, whose reelection Warren has endorsed. It will also be present in Warren's native Oklahoma, where Sanders will notably campaign Sunday.
Polls and crowd sizes have converged to put Warren in the middle of the conversation. Now we'll see if she has a plan for that, too.
Thousands of people from over 150 countries around the world are expected to participate in the "Global Climate Strike" on Friday. The list of co-sponsors for the domestic events alone is pages long and includes leading environmental advocacy organizations, faith-based organizations, for-profit business and political groups.
According to the strike's organizers hundreds of businesses in the U.S. -- Patagonia, Lush, Seventh Generation and Kickstarter -- will also close their doors, set up stations to support protesters or turn their screens green in solidarity.
New York City announced that public school students could skip classes and join marches without fear of repercussions. At least three 2020 Democratic presidential candidates have said formally that they plan to attend local protests as well.
The strike comes on the eve of a major U.N. Climate Summit in New York on Monday, following a brutal summer of extreme weather. Earlier this week, the Trump administration talked publicly about revoking California's regulatory waiver, which has allowed it to set separate, higher auto-emission and electric vehicle standards. The move is perhaps -- again -- a sign of this White House standing as an outlier on the global stage.
As Sanders hits the campaign trail in Iowa this weekend, he may be packing some sharper critiques for Biden. In an Instagram post on Thursday, the senator slammed the former vice president, who has consistently led in the polls.
"I like Joe, I've known him for many, many years. And the truth is he is against Trump, in my view, not a strong candidate," said Sanders. Later adding, "To beat Trump you need energy, excitement, large voter turnout. I think it is very hard to make the case that Joe Biden can generate that kind of energy."
ABC News' "Start Here" podcast. Friday morning's episode features ABC News Senior National correspondent Terry Moran and ABC News contributor John Cohen who sort through the fallout after an intelligence community whistleblower came forward with allegations against President Donald Trump. Then, ABC News' Stephanie Ebbs tells us how young climate activists are working to force the hands of companies when it comes to environmental issues. http://apple.co/2HPocUL
WHAT YOU NEED TO KNOW THIS WEEKEND
The public is welcome to attend a reception in Cokie Roberts' memory at the National Press Club, on the 13th floor, 529 14th St. NW in Washington on Friday from 6 p.m. to 8 p.m. And on Saturday, a funeral Mass will be held at the Cathedral of Saint Matthew the Apostle at 1725 Rhode Island Ave. NW in Washington at 10 a.m. The Mass will be streamed on ABC News Live as well.
President Donald Trump welcomes Australian Prime Minister Scott Morrison to the White House at 9 a.m. They hold a bilateral meeting at 10 a.m. and joint press availability at 11:45 a.m. Later, Trump hosts a state dinner in the Rose Garden at 8:20 p.m.
In Washington, thousands are expected to march from John Marshall Park to the Capitol Building as part of the "Global Climate Strike," starting at 11 a.m. Tom Steyer is expected to participate in Washington. Rep. Beto O'Rourke, D-Texas, is expected to participate in Denver. Former Housing and Urban Development Secretary Julián Castro is expected to participate in Cedar Rapids, Iowa.
Sen. Cory Booker, D-N.J., Montana Gov. Steve Bullock, South Bend, Indiana, Mayor Pete Buttigieg, Steyer and former Massachusetts Gov. Bill Weld speak at the MSNBC Climate Forum at Georgetown University starting at 9 a.m. on Friday.
Former Vice President Joe Biden, Booker, Buttigieg, Castro, Rep. Tulsi Gabbard, D-Hawaii, Sen. Kamala Harris, D-Calif., Sen. Amy Klobuchar, D-Minn., former Rep. Joe Sestak, D-Pa., Sen. Elizabeth Warren, D-Mass., and Marianne Williamson speak at the LGBTQ Presidential Forum at Coe College in Cedar Rapids, Iowa, at 7 p.m. (CST) on Friday.
O'Rourke participates in a gun violence roundtable in Denver on Friday. On Saturday, he appears on IPTV's Conversations with Presidential Candidates hosted by DMACC.
Sen. Bernie Sanders, I-Vt., campaigns in North Carolina and South Carolina on Friday. On Sunday afternoon, he travels to Norman, Oklahoma, for a rally, and later, he addresses the Comanche Nation Fair Powwow in Lawton.
Harris campaigns in Iowa on Friday and Saturday. On Saturday evening, she travels to Charleston to speak at the NAACP Freedom Fund Dinner. On Sunday, she campaigns in South Carolina.
On Saturday, Bennet, Biden, Booker, Bullock, Buttigieg, Castro, New York City Mayor Bill de Blasio, Gabbard, Harris, Klobuchar, O'Rourke, Rep. Tim Ryan, D-Ohio, Sestak, Steyer, Warren, Williamson and Andrew Yang will speak at the Polk County Democrats Streak Fry in Des Moines, Iowa, beginning at 11 a.m. (CST). Preceding the event, several candidates rally with supporters in Water Work Parks beginning at 9 a.m.
Also on Saturday, Buttigieg, Castro, Sanders and Warren speak at the Iowa's People's Forum at the Iowa Events Center in Des Moines beginning at noon. (CST).
On Sunday, in order of speaker, Gabbard, de Blasio, Bennet, Sanders, Ryan, Yang, Sestak, Bennet and Steyer participate in the Des Moines Public Schools and the Des Moines Register host "Youth Voice: The Iowa Caucus" at Roosevelt High School beginning at 8:30 a.m. (CST).
Also on Sunday in Iowa, Bullock and Sestak speak at the Story County Democrats' Fall Barbecue beginning at 5 p.m. (CST).
Bennet, Castro and Sestak campaign in Iowa all weekend.
Biden has a town hall in Iowa on Friday. He travels to St. Louis on Sunday.
Booker has a meet-and-greet event in Iowa on Saturday.
Bullock, Buttigeig, O'Rourke and Sanders make multiple campaign stops in Iowa on Saturday and Sunday.
Sunday on ABC's "This Week": A special tribute honoring the life and legacy of Cokie Roberts, with Sam Donaldson and George Will. Plus, Martha Raddatz goes one-on-one with former Defense Secretary James Mattis. And the Powerhouse Roundtable discusses all the week's politics and remembers Cokie Roberts, with ABC News Correspondent Karen Travers, former Democratic National Committee Chairperson and Fox News Contributor Donna Brazile, NPR National Political Correspondent and Fox News Contributor Mara Liasson and Washington Post Political Columnist Karen Tumulty.
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The Note is a daily ABC News feature that highlights the day's top stories in politics. Please check back tomorrow for the latest.