The Note: Trump stirs debates in Congress with Iran, Iraq moves

House leaders are intent on probing the circumstances of the attack.

The TAKE with Rick Klein

It's probably not reasonable to expect clarity to emerge out of a dangerous muddle of a moment.

A "Gang of Eight" briefing for congressional leaders Tuesday on the operation to kill Qassem Soleimani will be followed with broader updates for members of Congress on Wednesday -- enough to pull the senators who are running for president off the campaign trail.

House leaders are intent on probing the notion that an "imminent" attack was headed off. They'll also look to debate and perhaps limit Trump's powers to conduct future strikes -- testing the notions that he didn't have to tell them about the Soleimani operation in advance, and that his tweets serve as sufficient legal notification in the future.

Members of both parties have agreed in the past on the need for Congress to reassert itself in military matters.

It remains to be seen whether bipartisanship will prevail in a political environment dictated at least in part by impeachment.

But this is about more than a campaign talking point. An administration with severe credibility issues on Capitol Hill may have to draw on goodwill that's somewhat depleted at the moment.

The RUNDOWN with MaryAlice Parks

Senators on Monday continued to debate the definition of an impeachment trial, after a highly coveted, potential star witness said in a statement that he would, in fact testify, if subpoenaed.

It would take four Republicans voting with Democrats to subpoena Bolton. He would, in theory, have firsthand knowledge of the Ukraine affair laid out in the first article of impeachment and could provide insights into the president's state of mind during the time in question -- something Republicans have said was lacking in the Democrats' case so far.

After all, one of the central questions of the impeachment has been whether Trump was concerned with corruption in Ukraine that could harm U.S. interests or whether he was primarily concerned with carving out a political advantage over a rival and thus engaging in more nefarious activity.

Sen. Marco Rubio tweeted that the Senate did not need to hear new testimony, "Our job is to vote on what the House passed, not to conduct an open ended inquiry." To which Sen. Brian Schatz responded, "Nonsense."

Unsurprisingly, two key senators to watch -- Sens. Susan Collins and Mitt Romney -- both seem to agree that Bolton would be a relevant witness.

The TIP with Lissette Rodriguez

Just four days after he announced the end to his own presidential bid, former Housing and Urban Development Secretary Julián Castro endorsed Democratic presidential candidate Sen. Elizabeth Warren on Monday morning. Neither hesitated to highlight their years-long relationship or their connections to President Barack Obama in respective emails to supporters.

"Julián and I both had the honor to serve in President Obama's administration, where we had the opportunity to work on a number of issues that touch people's lives," Warren wrote in her email, while Castro highlighted their work to increase housing opportunities.

The endorsement comes just as Warren's campaign aims to build out a ground game in Castro's home state of Texas and just as an impeachment trial threatens to take her off the trail. But it doesn't end there. Castro is already scheduled to host a joint rally with Warren at Brooklyn's King Theatre in New York City and Castro's communications director Sawyer Hackett told ABC News that there are more joint and solo events to come, with a focus on early states, and -- especially -- if and when Warren has a Senate impeachment trial to attend.

Hackett also noted a number of former Castro campaign staffers have moved to work for Warren's campaign, including a former organizing director, director of scheduling and advance, and state staffers who fell victim to cutbacks as Castro's campaign struggled with fundraising.

ONE MORE THING

John Bolton, the former national security adviser, has emerged as an impeachment trial wild-card, putting pressure on Senate Republicans to allow witnesses. While it's considered highly unlikely that enough Republicans will break from their party to oust President Donald Trump -- two thirds of the Senate would be needed to remove the president from office -- only 51 votes are needed to demand witnesses or documents. "When the time comes, if 51 senators want to hear Ambassador Bolton, I think that's fine," said Sen. John Cornyn, R-Texas. Read more of this ABC News analysis.

THE PLAYLIST

ABC News' "Start Here" Podcast. Tuesday morning's episode features ABC News Chief Global Affairs correspondent Martha Raddatz, who checks in from Tehran, Iran, where a massive funeral procession for Iranian general Qassem Soleimani. Then, ABC News Chief White House correspondent Jonathan Karl tells us why President Donald Trump is not backing down from his threat to potentially strike cultural sites if Iran retaliates. And, ABC News Senior Congressional correspondent Mary Bruce explains why John Bolton is now willing to testify in a potential impeachment trial. http://apple.co/2HPocUL

FiveThirtyEight Politics Podcast. Late Thursday, the Pentagon announced that the United States killed Iran's Maj. Gen. Qassem Soleimani, "at the direction of the President" in an airstrike in Iraq. Iran has since vowed retaliation. In this installment of the FiveThirtyEight Politics podcast, the crew discusses how the current conflict or any further escalation could reshape the dynamics of the 2020 election. https://apple.co/23r5y7w

WHAT YOU NEED TO KNOW TODAY

  • Sen. Elizabeth Warren, D-Mass., appears on ABC's "The View" and then holds a campaign event with former Housing and Urban Development Secretary Julián Castro in New York City at 5 p.m.
  • Former South Bend, Indiana, Mayor Pete Buttigieg holds fundraising events in Houston at 11:30 a.m. and then Dallas at 6 p.m.
  • Rep. Tulsi Gabbard, D-Hawaii, holds a town hall in Northfield, New Hampshire at 6 p.m.
  • Sen. Amy Klobuchar, D-Minn., gives remarks at the College Convention 2020 at 10:30 a.m. in New Hampshire and then holds a fundraising event in Washington, D.C. at 7 p.m.
  • Former New York City Mayor Michael Bloomberg has coffee with the mayor of Richmond at 8:45 a.m. and then holds media availability at 10 a.m. in Richmond, Virginia.
  • Former Massachusetts Gov. Deval Patrick beings his day with an event at Barbershop Grooming Lounge at 10:30 a.m., a visit to Turning leaf Project at 3:45 p.m. and then a campaign event at 4:30 p.m. in South Carolina.
  • Former Vice President Joe Biden holds a fundraiser and delivers remarks in New York City and holds a fundraiser in Gladwyne, Pennsylvania, in the evening.
  • Cory Booker, D-N.J. hold a Black Women's Luncheon at 12 p.m. and a Meet and Greet at 3:30 p.m. in Des Moines, Iowa.