WASHINGTON — Things were on a clear course as far as President Trump’s re-election campaign was concerned. The impeachment proceedings unfolding on Capitol Hill had proved to be a boost for volunteer recruitment and small-dollar donations. The year ended with a blockbuster jobs report and the unemployment rate falling to 3.5 percent, its lowest level since 1969.
Mr. Trump was ready to aggressively attack a Democratic field he and his advisers viewed as weak across the board. Few if any of the president’s top campaign aides were looking to change the channel.
But Mr. Trump’s decision to authorize the killing of Maj. Gen. Qassim Suleimani, which he has described to friends and allies as a necessary action he was forced to take, has opened up a more uncertain political reality as the president enters an election year. That uncertainty was on display Tuesday night when Iran fired missiles at American forces in Iraq, in its first act of retaliation.
Some advisers have highlighted to Mr. Trump the short-term lift the strike could give his re-election prospects, and his campaign has run nearly 800 distinct Facebook ads trumpeting the killing, according to Acronym, a progressive digital strategy group. The ads refer to Mr. Trump’s “leadership as commander in chief” and direct voters to an “Official Trump Military Survey,” which acts as a portal to his campaign website.
But whether the strike will help the president win over more voters rests on factors largely outside Mr. Trump’s control. How Iran retaliates, and how voters who responded to his 2016 campaign message about ending “forever wars” in the Middle East react to a potentially escalating conflict are the two most immediate questions.
“One of the major parts of the Trump coalition is voters who after the wars in Iraq and Afghanistan wanted to be much more cautious engaging in an assault with ground troops,” said Matt Schlapp, the chairman of the American Conservative Union. “There’s a significant number of libertarians and people who are weary about casually getting involved in a conflict with an Arab country that can take decades to resolve.”
In the days since the attack, Mr. Trump has soaked up praise from Republican senators and allies, and aides described him as very comfortable with his decision. Mr. Trump, who has been eager to bask again in the kind of praise he received after ordering the military to bomb Syrian government forces after they used chemical weapons in 2017, has enjoyed his victory lap. He even described in graphic detail to friends the attacks on the American Embassy in Baghdad that preceded the strike against General Suleimani.
Mr. Trump pointed out to one person who spoke to him on the phone last week that he had been pressured to take a harder line on Iran by some Republican senators whose support he needs now more than ever amid an impeachment battle. He also indicated that one of his top motivations for the strike was to protect Israel.
Still, he resisted entreaties last week from his son-in-law, Jared Kushner, to deliver a televised address on the raid, aides said. A White House spokesman did not respond to an email about Mr. Kushner.
In his phone conversation last week, Mr. Trump responded that no one knew where things would end when the caller expressed concern that General Suleimani’s death could end up starting a war. And he is aware as well of the consequences for his own political future, even while projecting confidence in his decision.
The president and his aides have tried to use the response of Democratic presidential candidates as another example of how far left the party’s field has tacked.
“He was a monster. And he’s no longer a monster; he’s dead,” Mr. Trump told reporters in the Oval Office on Tuesday, adding: “I don’t hear too many people other than politicians who are trying to win the presidency. Those are the ones that are complaining. But I don’t hear anybody else complaining.”
The Republican National Committee, meanwhile, has targeted 2020 Democratic candidates like Senators Bernie Sanders and Elizabeth Warren, both of whom have called the strike a dangerous escalation.
In the case of Ms. Warren, some Trump advisers noted that she had initially called General Suleimani a “murderer,” a statement for which she was attacked by some liberal critics.
“In a matter of a few months, the president has taken out two of the most wanted terrorists without American casualties,” Kellyanne Conway, a top adviser to Mr. Trump, said of General Suleimani and Abu Bakr al-Baghdadi, the ISIS leader killed by American forces in October.
“That’s simple and easy to explain and it has forced the Democrats and the professional left to do some convoluted explaining of how removing terrorists makes us more susceptible to terrorism.”
Other administration officials have made a more direct comparison with General Suleimani and Mr. al-Baghdadi. Instead of acknowledging his title, “general,” they have focused on his terrorist activities and the number of people whose deaths he was responsible for over the years.
But even those allies who have pressed Mr. Trump to confront Iran expressed uncertainty about what is to come, especially when the administration has struggled to explain what it is doing in the days since the strike.
One Republican Senate staff member described an afternoon spent phoning the Defense Department to get more information about a draft letter from a senior military officer that suggested plans for a troop withdrawal from Iraq were underway.
The answer he received was that Pentagon officials had only seen it on Twitter. It was the Iraqi Embassy that eventually confirmed to the Senate staff members that the letter was, in fact, real, before the chairman of the Joint Chiefs of Staff, Gen. Mark A. Milley, called an urgent news conference to make it clear that sending the letter had been an “honest mistake.”
Some officials have highlighted an interview that Gen. David H. Petraeus gave Sunday on CBS’s “Face the Nation” as the best defense yet of Mr. Trump. General Petraeus, who has criticized key administration decisions about Middle East policy, described the killing of General Suleimani as “bigger than Bin Laden” and “bigger than Baghdadi.”
Yet the explanations of what took place have not included key details, or any description of the quality of the intelligence that officials have said led to Mr. Trump’s order.
Democrats say that Mr. Trump’s decision to carry out a strike that two previous presidents had deemed to be too risky will be used against him by voters.
Mr. Trump’s action on Iran “reinforces his weaknesses,” said Geoff Garin, a Democratic pollster, and played into a view of Mr. Trump as a rash decision maker. Voters, he said, are “very likely to think about his conduct in Iran through that prism.”
Tim Murtaugh, a spokesman for the Trump campaign, said he disagreed. “Americans want to see their president acting decisively and defending the nation’s interests, and that’s exactly what President Trump did,” Mr. Murtaugh said. “Democrats and much of the media risk appearing as Iran apologists who look to blame America for responding to terrorist acts and plans.”