“We would be powerless if we didn’t get the majority, but the country gave us the majority in the House of Representatives,” he added.

The resolution is expected to easily pass the House as early as Wednesday, with nearly every Democrat likely to support it. Adoption will force a vote on the Senate floor in the coming days, because it is privileged and guaranteed a vote under congressional rules. Democrats hope it will pose a tough loyalty test for Republicans, who were also mostly blindsided by Trump’s strike.

But the House and Senate GOP are likely to remain largely united on the floor, with many across the party rallying around Trump’s slaying of the Iranian major general linked to the deaths of hundreds of Americans.

Senate Democrats will need at least four Republicans to join them if all 47 caucus members vote for the resolution. Such a break would mark a repudiation of Trump as he gears up for his reelection campaign and an impeachment trial in the Senate.

A handful of Republicans — including vocal war skeptics like Sens. Rand Paul of Kentucky and Mike Lee of Utah — have bucked their party in the past, protesting what they see as the unchecked military might of the executive branch. But it’s not clear they would oppose Trump in this case.

Several Republicans are already suggesting the debate over the Iran measure could look very different from the bipartisan resolution last year that would have ended U.S. support for the deadly conflict in Yemen.

The war powers resolution getting a vote this week would essentially end additional military operations in Iran unless there is the threat of an imminent attack — a much tougher measure for Republicans to support. It would require the Trump administration to cease all military activity in Iran within 60 days unless congressional approval was given.

House GOP leadership aides are expecting only a handful of defections on the floor.

“There shouldn’t be a single Republican member of our conference [to] vote for this resolution, which has nothing to do with the AUMF debate and everything to do with politics,” Rep. Mark Meadows (R-N.C.) told POLITICO referring to the Authorization for Use of Military Force. “When President Obama intervenes in Syria, Pelosi says nothing! When President Trump takes out a terrorist with a drone, she sides with the opposition.”

“There shouldn’t be a single Republican member of our conference [to] vote for this resolution, which has nothing to do with the AUMF debate and everything to do with politics,” Rep. Mark Meadows (R-N.C.) told POLITICO. | Alex Wong/Getty Images

On Wednesday, lawmakers will receive a full briefing from Trump officials, including Defense Secretary Mark Esper and Secretary of State Mike Pompeo, according to a notice sent to congressional offices.

The House resolution, announced by Speaker Nancy Pelosi late Sunday, opens yet another front against Trump, who has repeatedly ignored congressional leaders of both parties in his foreign policy across the Middle East.

Pelosi described Trump’s action as a “provocative and disproportionate military airstrike” that she said endangers U.S. troops “by risking a serious escalation of tensions with Iran.”

House Democrats have condemned Trump in droves, with the caucus’ most liberal members, like Rep. Barbara Lee of California, as well as moderate ex-military members like Jason Crow of Colorado, equally forceful in their opposition.

“I'm not trying to be secretary of State. I'm trying to understand if we, as a nation, should be having a conversation if we want to get into another protracted war in the Middle East,” Rep. Elissa Slotkin, an Iraq War veteran who will lead the resolution on the floor this week, said on MSNBC’s “Morning Joe” on Monday.

The resolution comes with some risk for Pelosi and her deputies in the House, however. Top Democrats are anxious that Republicans could use the measure to force a vote on another contentious issue, like Israel, that has split the Democratic Caucus in the past, according to people familiar with the discussions.

Trump’s acceleration of the U.S.-Iran conflict could become a major theme of the House Democratic agenda in 2020, with the three-month impeachment probe now behind them.

Top Democrats are planning to step up their oversight of Trump’s actions in Iran and the Middle East generally. House Intelligence Chairman Adam Schiff said Monday he plans to hold open hearings on what he sees as a rapidly escalating threat to U.S. interests in the region.

“I think there should be open hearings on this subject,” Schiff told The Washington Post. “The president has put us on a path where we may be at war with Iran. That requires the Congress to fully engage.”

Schiff’s office declined to comment on next steps on oversight, which is also likely to involve the House Foreign Affairs Committee and the House Armed Services Committee.

With Democrats trying to bolster their messaging by elevating ex-military members like Slotkin, Republicans, too, are leaning on their veterans to help make their case. Some of the GOP members who have praised Trump’s airstrike on Soleimani on cable news in recent days include Reps. Mike Gallagher of Wisconsin, Adam Kinzinger of Illinois and Michael Waltz of Florida.

“I’m not sure why the Democrats have chosen to go so deep in opposition to this. While it may work with their base, most Americans don’t see this fear of Iran as a good look,” Kinzinger said. “If in time Iran backs down and moderates, the Democrats will be seen as on the wrong side of this, relatively soon. If they continue attacking Americans, people will be even angrier at Iran’s continued provocations.”

Republicans are also using the opportunity to draw another contrast with Democrats amid the impeachment battle.

“While Democrats are trying to remove President Trump from office, the President is focused on removing terrorists from the face of the earth,” tweeted House Minority Leader Kevin McCarthy (R-Calif.).

Think of the contrast. ↴

While Democrats are trying to remove President Trump from office, the President is focused on removing terrorists from the face of the earth. — Kevin McCarthy (@GOPLeader) January 5, 2020

Khanna said he hoped Republicans would support the resolution later this week, noting the bipartisan coalition he spearheaded earlier this year that successfully passed a war powers resolution cutting off U.S. support for the war in Yemen. Trump promptly vetoed the measure — which drew support from 16 Republicans in the House and seven Republicans in the Senate — marking only the second veto of his presidency.

But Khanna argued many of those same Republicans should be willing to support this resolution, even amid the partisan warfare currently unfolding over Democrats’ decision to impeach Trump over abuse of power and obstruction of Congress charges in the Ukraine scandal.

The California Democrat is also pushing for a vote on his bill to defund U.S. military action in Iran that doesn’t first receive congressional approval. Khanna and GOP Rep. Matt Gaetz introduced a similar amendment this summer that was adopted in the House’s annual defense authorization bill with 27 Republicans breaking with their party to support it.

But that provision — along with an amendment from Lee to repeal a 2002 military authorization passed in the run-up to the invasion of Iraq — was stripped out during final negotiations in December, over the howls of progressives.

“The Pentagon fought tooth and nail — tooth and nail — to get that Iran amendment out. It was their highest priority. And that to me was a signal that they were planning something at some time,” Khanna said. “But once we passed the NDAA and we did not get their commitment to restrict action in Iran, they took that as a blank check. And it was a colossal mistake.”

Members of the Congressional Progressive Caucus, including Khanna, huddled on a call Sunday to talk about a strategy on Iran going forward. The call was held before Pelosi announced the vote on the war powers resolution.

The CPC heard from Trita Parsi, a prominent Iran analyst and co-founder of the Quincy Institute for Responsible Statecraft, who urged liberals to move responsibly to end U.S. entanglements in the Middle East.

Connor O'Brien contributed to this report.