WASHINGTON — President Trump’s abrupt decision to kill Iran’s top security commander has reshuffled the already fraught political dynamic around impeachment and thrust matters of war and peace into the middle of an election-year debate over whether to remove Mr. Trump from office.
As Congress reconvenes on Monday, the specter of escalating hostilities with Iran and a searing debate over the justification behind Mr. Trump’s action will take center stage on Capitol Hill. The unexpected turn of events has added a volatile new element to the pitched fight over Mr. Trump’s impeachment trial in the Senate.
For Republicans, the killing of Maj. Gen. Qassim Suleimani, the leader of Iran’s elite Quds Force, fueled a new line of defense of the president, as they argued that Democrats’ effort to oust Mr. Trump while he tended to matters of national security was irresponsible.
“Think of the contrast,” Representative Kevin McCarthy of California, the top House Republican, wrote on Twitter on Sunday. “While Democrats are trying to remove President Trump from office, the President is focused on removing terrorists from the face of the earth.”
Democratic leaders insisted the two issues must not be interwoven, and said that lawmakers were obligated to follow through with the impeachment process even as they debated the way forward on Iran. Many of their rank and file have charged that Mr. Trump authorized the strike precisely to distract attention from the charges at the center of his impeachment.
“Congress has to do both of our constitutional responsibilities,” said Senator Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee.
“One, to protect the American people and be a coequal branch of government with the administration to make sure that we keep Americans safe,” he added on NBC, referring to Iran. “Secondly, we also have to take on the responsibility of what’s going to come over at some point from the House, and that’s to conduct a full and fair trial.”
Related or not, the rapid developments in recent days mean that Congress will grapple simultaneously in the coming weeks with two of its most consequential constitutional duties: the power to impeach and to weigh matters of war. The outcome will clarify the legislative branch’s appetite for checking an expansive presidency and will also likely play a continuing role in Mr. Trump’s fight for re-election.
The timing and outlook for the president’s impeachment trial were already murky. In a pair of votes in December, the House impeached Mr. Trump for abuse of power and obstruction of Congress. The charges stem from his bid to pressure Ukraine to investigate his political rivals, while withholding nearly $400 million of military aid.
Speaker Nancy Pelosi has refused to transmit the charges against Mr. Trump to the Senate, in a bid to give Senate Democrats more leverage as they try to force Republicans to agree to call administration witnesses and gain access to more documents. The president blocked administration officials from testifying in the House inquiry and refused to turn over documents that impeachment investigators requested, prompting the obstruction charge.
Now, the question is whether the coming debate on Iran will affect the calculations by Democrats and Republicans strategizing over the terms and length of a trial.
Democrats on the left argue that the impulses that led Mr. Trump to strike General Suleimani are themselves grounds for his removal.
“The issues are connected,” said Representative Ro Khanna, Democrat of California, who sponsored legislation to block Mr. Trump from launching an unauthorized strike against Iran. “It shows the same reckless pattern of policymaking that he engaged in with Ukraine. It’s no longer a matter of standing up for the rule of law and the Constitution. This is a matter of safeguarding our national security and peace because a president that disregards constitutional processes can pose a huge risk to stability and peace.”
Senators spent the year-end holidays preparing for the impeachment trial, a showdown over the fate of Mr. Trump’s presidency that could consume parts of January and February.
Lawmakers and aides close to Ms. Pelosi say she has not yet made up her mind on how or when to proceed, and said foreign policy would not affect her thinking. A decision could come as soon as this week, when House lawmakers reconvene on Tuesday and the speaker holds a series of meetings with her leadership team.
But the strike on the Iranian general was preoccupying many lawmakers. Some Democrats, calling the action unauthorized and illegal, made clear over the weekend that they intended to try to curtail Mr. Trump’s ability to strike Iran in the future. After the White House on Saturday sent Congress an unusual, completely classified notification of the drone strike, Ms. Pelosi said it raised “serious and urgent questions” about the decision.
“Congress and I will do everything I can to assert our authority,” Senator Chuck Schumer of New York, the Democratic leader, said Sunday on ABC. “We do not need this president either bumbling or impulsively getting us into a major war.”
But in a clear signal that he has no interest in consulting with Congress on his military moves or strategy, Mr. Trump suggested on Sunday that lawmakers should monitor social media to discern how he plans to proceed.
“These Media Posts will serve as notification to the United States Congress that should Iran strike any U.S. person or target, the United States will quickly & fully strike back, & perhaps in a disproportionate manner,” the president tweeted. “Such legal notice is not required, but is given nevertheless!”
Senators are expected to receive a full briefing from administration officials in the coming week on the strike. An all-members briefing in the House has yet to be scheduled, according to a senior Democratic aide.
Senators could be forced to vote on the scope of the president’s war-making powers with Iran as soon as mid-January. The House could do so on a similar schedule, though it is not clear whether Congress has the appetite for a full debate over war powers, or whether lawmakers will be able to reach a consensus.
That timing could collide directly with an impeachment trial, an all-consuming proceeding that brings other Senate work to a halt.
Though they did not explicitly connect the two issues, Republicans have begun looking for ways to force Ms. Pelosi’s hand and move the trial along. Senator Lindsey Graham of South Carolina said on Sunday that he would seek a long-shot change to the Senate rules to compel the House to bring its case forward so it could be dispensed with quickly.
“If we don’t get the articles this week, then we need to take matters in our own hands and change the rules. Deem them to be delivered to the Senate,” he said on Fox News.
In an interview on Sunday evening, Representative Steve Scalise of Louisiana, the No. 2 House Republican, said that the strike “puts more pressure” on Ms. Pelosi to put aside impeachment and focus on “things that really matter.”
“It’s time to let the Senate do its job and move on because there are real, significant issues that the country is facing right now — both foreign and domestic,” Mr. Scalise said.
Democratic leaders insisted on Sunday that Congress owed it to the country to air what they believe are serious charges of high crimes and misdemeanors against Mr. Trump. They chastised Republicans, saying they were seeking to use the threat of war to paper over the president’s wrongdoing.
“It’s complicated, but I do think they are separate responsibilities,” Representative David Cicilline, Democrat of Rhode Island, said in an interview. “And while the president may hope that there is some effort to set aside the impeachment while we try to figure out how to avoid going to war with Iran, we have to do both at once.”
Across the political spectrum, Democrats’ response to the escalation in Iraq and Iran underscored the deep mistrust between their party and Mr. Trump. Some liberal lawmakers have begun questioning whether Mr. Trump’s decision to kill General Suleimani could have been influenced by his desire to neutralize the impeachment threat against him.
“It is a reasonable question to ask, particularly when the administration, immediately after having taken this decision, offers a bunch of contradictory explanations for what’s going on,” Senator Elizabeth Warren of Massachusetts, one of the Democrats vying for her party’s nomination to challenge Mr. Trump, said Sunday on CNN.
Liberals like Mr. Khanna may also push the debate toward a place Ms. Pelosi had sought to avoid by conflating specific impeachment charges the speaker argues are separate from Mr. Trump’s other behavior with foreign policy decisions they do not like.
About a dozen progressive advocacy groups planned to converge on the Senate daily beginning on Monday to demand Mr. Trump’s removal from office, rallying not just around the charges against him but against military escalation.
For now, at least, the debate over the procedures of a Senate trial has continued on its own track. With his counterpart, Senator Mitch McConnell of Kentucky, unwilling to negotiate, Mr. Schumer on Sunday began explicitly appealing to a handful of moderate Republicans who Democrats believe could join them in voting to call witnesses once the trial begins.
“McConnell will not go for a fair trial,” Mr. Schumer said on ABC. “You can’t have a fair trial without witnesses and documents, particularly those that were right at the scene of the charges. But four Republican senators can join us.”