The Note: Beto O'Rourke sparks debate about Obama legacy for Democrats As Obama learned in time, the idea of Beto O'Rourke may not match the realities.

The TAKE with Rick Klein

The most diverse Democratic primary field in history could be influenced by the moves of two white men -- both of whom may seek to claim the legacy of the first African-American president.

Amid that political thicket, Joe Biden may have the strongest credentials, after two terms as President Barack Obama's vice president and decades of service to Democratic Party causes. One more big political speech this week -- coming Saturday in his home state of Delaware -- will only stoke expectations further.

But first comes Beto O'Rourke. The former Texas congressman, who announced his presidential candidacy early Thursday, is scheduled to be in Iowa Thursday through Saturday, with several of stops in places Democrats now know as Obama counties that flipped to President Donald Trump.

O'Rourke is a well-off white man in a year the party base may not value such attributes. It's an odd combination to consider as a political vulnerability, but one he is conceding -- at least in part.

"The government at all levels is overly represented by white men," he told Vanity Fair in a new cover story. "That's part of the problem, and I'm a white man."

O'Rourke's background won't be mistaken for Obama's -- or that of Sen. Cory Booker, Sen. Kamala Harris, or anyone else in the field. And as Obama himself learned in time, the idea of him may not match the realities revealed by a campaign.

The RUNDOWN with MaryAlice Parks

The Senate stands to deliver the president a major rebuke Thursday.

The upper chamber will vote on a resolution to terminate Trump's national emergency declaration, which he signed to re-allocate military funds outside of the congressional appropriations process in order to build more barriers on the southern border.

The resolution is expected to pass, with at least five Republicans having publicly declared their intent to support it. Several other Republicans also have said they think the president is pushing it with this move, and efforts to find an alternative measure for GOP senators to register some disapproval without rejecting the president's plan went nowhere.

While neither the House nor the Senate likely has the votes on this issue to override a veto, it will still be monumental if Trump uses his veto power for the first time -- as he said he plans to do -- in order to scrap a bill that, at its core, is the legislative branch telling him he's overstepped his authority.

The TIP with Adam Kelsey

Three of America's most prominent black politicians -- two of whom are running for president and third who's considering it -- will all be in the same place Thursday, the Bold v. Old conference in Washington.

The event isn't a forum for ideas about race, rather one about economic policies to address inequality -- an issue that disproportionately affects minorities, but one that also transcends demographics and political identity. The simple fact is that Sens. Booker and Harris, and former Georgia gubernatorial candidate Stacey Abrams, have become three of their party's leading voices on such issues and who, while embracing their identities, are also seeking not to be defined by them as they continue to work their way toward the White House.

In a presidential cycle already featuring the most diverse field in American history, Thursday's event is the latest opportunity for the candidates to define their platforms by more than what meets the eye.

THE PLAYLIST

ABC News' "Start Here" Podcast. Thursday morning's episode features ABC News Senior Transportation correspondent David Kerley, who tells us why the Federal Aviation Administration decided to ground all 737 Max 8 and 9 planes in the U.S. Then, ABC News' Trish Turner and Aaron Katersky examine Paul Manafort's latest prison sentence and the newest batch of financial charges brought against him in New York. http://apple.co/2HPocUL

WHAT YOU NEED TO KNOW TODAY

The president meets with the prime minister of Ireland starting at 10:50 a.m. in the Oval Office. He then travels to the U.S. Capitol for the Friends of Ireland Luncheon at 2 p.m. In the evening, the prime minister of Ireland returns to the White House to deliver the "Shamrock Bowl Presentation" at 6 p.m. to the president and first lady.

Roger Stone, a veteran political operative and longtime friend of the president, appears in district court at 10 a.m. in Washington.

Sens. Kamala Harris, D-Calif., Cory Booker, D-N.J., Sherrod Brown, D-Ohio, and former Georgia gubernatorial candidate Stacey Abrams speak at the "Bold v. Old" conference in Washington. Activities start at 9 a.m.

The House Oversight Committee discusses "ongoing preparations for the 2020 Census and the addition of a citizenship question" with Secretary of Commerce Wilbur Ross at 10 a.m. on Capitol Hill.

The Senate is expected to vote Thursday afternoon on H.J. Resolution 46, an effort to terminate Trump's national emergency proclamation.

Former U.S. Rep. Beto O'Rourke travels to Iowa for a meet-and-greet in Muscatine.

Download the ABC News app and select "The Note" as an item of interest to receive the day's sharpest political analysis. Please check back tomorrow for the latest.