WASHINGTON — Washington plunged into political war Wednesday in the wake of a split decision by voters in the midterm elections, with President Trump ousting his attorney general and threatening to retaliate against Democrats if they launch investigations into his personal conduct and possible corruption in the administration.

The rapid shift to battle stations signaled the start of what is likely to be two years of unremitting political combat as Trump positions himself for re-election. For the first time, Trump will be forced to navigate divided government as Democrats who won the House pledge to be a check on his power and face pressure from their liberal base to block him at every turn.

The acrimony was punctuated by Trump’s bombast, as the president refused to show contrition or take responsibility for his party’s washout in many suburban areas where voters who previously backed Republicans rejected the president’s hard-line politics.

House Minority Leader Nancy Pelosi, Calif., who is poised to lead the new Democratic majority as speaker, said her caucus would use its subpoena authority to pursue sweeping oversight of the Trump administration.

“We will have a responsibility to honor our oversight responsibilities, and that’s the path that we will go down,” she told reporters. But, she added, Democrats would do so in the interest of “trying to unify our country.”

Senate Minority Leader Charles Schumer, D-N.Y., whose party lost seats in the upper chamber, nonetheless cheered the House triumph and said, “There’s now a check on Donald Trump, and that is great news for America.”

In the wake of Tuesday’s midterms, some allies said, Trump was both emboldened – because he believed he had helped expand the Republican majority in the Senate – and apprehensive, because he would no longer be able to bend all of Congress to his will.

But unlike his predecessors who acknowledged a “shellacking” (Barack Obama in 2010) or a “thumpin'” (George W. Bush in 2006) after midterm losses, Trump spun his own reality by claiming “very close to complete victory.”

Trump said in a wide-ranging and often sharp-tongued news conference that any hope for bipartisan deals will evaporate if House Democrats use their new power to investigate him or his administration. Such efforts, he said bluntly, would precipitate “a warlike posture.”

House Democrats have said they plan to begin a series of investigations of the president, including issuing a subpoena for his tax returns, which he has for years refused to release. Trump said he would respond by using the Republican-controlled Senate as a cudgel, instructing his allies there to investigate alleged misconduct by Democrats.

“They can play that game, but we can play it better, because we have a thing called the United States Senate,” Trump said. “They can look at us, then we can look at them and it’ll go back and forth. And it’ll probably be very good for me politically . . . because I think I’m better at that game than they are, actually.”

Senate Majority Leader Mitch McConnell, R-Ky., on Wednesday dodged a reporter’s question about what Senate Republicans would do if House Democrats try to investigate Trump.

“The Democrats in the House will have to decide just how much presidential harassment they think is good strategy,” McConnell told reporters. “I’m not so sure it will work for them,” he added, noting that Republican investigations of President Bill Clinton in the late 1990s backfired politically.

McConnell is trying to position the Senate as a stable front for conservative governance and to stay out of the political firefight between Trump and House Democrats, according to his advisers. As the Senate leader told reporters, his top priority will continue to be confirming conservative nominees to federal courts, which Republicans have done at a record pace in the last two years.

Trump has told advisers that he intends to exploit divisions among House Democrats, according to a senior White House official. He believes he can pit Pelosi and others who are interested in making deals with him on policies like infrastructure spending against those who rose to office intent on blocking his agenda and, perhaps, beginning impeachment proceedings.

The president’s allies argued that Democrats were overestimating their mandate from Tuesday’s elections and will emerge as a useful political foil for Trump as he seeks reelection.

“I feel sorry for the Democrats because he’s going to crush them,” former Trump deputy campaign manager David Bossie said. “These people hate him more than they want to do their jobs, and that’ll allow him to be reelected in 2020.”

Trump also has said privately that he does not believe his administration should necessarily cooperate with Democratic investigations, and that he would be willing to fight subpoenas to the Supreme Court if necessary, according to the senior White House official and an outside adviser to the president, both of whom spoke on the condition of anonymity to share internal discussions.

Trump has been consulting White House lawyer Emmet Flood, who is overseeing the handling of the Russia investigation, and Flood has expressed interest in fighting back against incoming subpoenas, according to the outside adviser.

But Trump’s confidence in his own ability to navigate the thicket of obstacles facing him will soon be tested, according to Republicans from past administrations who recall being humbled by congressional Democrats winning power. The deluge of legal scrutiny and congressional subpoenas risks overwhelming the president’s agenda.

“One of the things the White House needs to understand is that we doubled the size of the general counsel’s office and that wasn’t big enough,” former top George W. Bush adviser Karl Rove said about the Democrats’ sweep in the 2006 midterm elections. “We found out pretty quick that we didn’t have enough lawyers.”

The White House Counsel’s Office is undergoing a transition. Pat Cipollone only recently took over from Donald McGahn as counsel and has a number of vacancies to fill. The adviser described the office as “in desperate need” of recruiting more attorneys. Many experienced lawyers at top Washington firms have long been reluctant to join the White House, both because they would have to take a pay cut and because of the chronic turmoil inside.

CLASH WITH REPORTERS

During his remarkably combative news conference in the East Room of the White House on Wednesday, Trump repeatedly lost his cool as he answered questions from journalists for 86 minutes. He called CNN’s Jim Acosta “a rude, terrible person,” snapped at Peter Alexander of NBC News and directed April Ryan of American Urban Radio to “sit down.” And when Yamiche Alcindor of “PBS NewsHour” asked the president whether by identifying as a “nationalist” he also was embracing the label “white nationalist,” he told her repeatedly, “That’s such a racist question.”

“To say what you just said is so insulting to me,” Trump responded to Alcindor, who is black.

Trump also was cutting in his criticism of some House Republicans who lost re-election, singling them out by name and attributing their losses to their decisions to distance themselves from him.

“Mia Love gave me no love, and she lost,” Trump said, referring to the defeated Utah congresswoman who was the lone black Republican woman in the House. In a mocking tone, he continued, “Too bad. Sorry about that, Mia.”

Trump also told reporters that he believes his chances of striking deals – such as to fund building projects, lower the prices of prescription drugs and refashion trade policies – would be greater with a divided Congress. He said he looks forward to working with Pelosi on “a beautiful bipartisan-type situation.”

Sen. Robert Casey Jr., D-Pa., who was re-elected Tuesday in a state that Trump carried in 2016, said, “It’s in his interests, even with the preoccupation with investigations or the back and forth, to show he can move the country forward. People are pretty exhausted with the back and forth.”

Rep. Mark Meadows, R-N.C., a confidant of Trump and head of the conservative House Freedom Caucus, said, “The president has always been about making a deal. I think you’re going to see a lot more engagement with Congress.”

Still, Meadows said, he has not “heard any consternation or concern expressed by my colleagues that the president will govern in a way that is not conservative.”

HOT AND COLD

After demonizing Democrats in apocalyptic terms and attacking Pelosi on the campaign trail, Trump said Wednesday, “The election’s over. Now everybody is in love.”

But Trump drowned out his own call for unity within hours by announcing via Twitter the sudden ouster of Attorney General Jeff Sessions, who said in his resignation letter that the president had directed him to resign.

The two parties plunged into a fierce disagreement over whether the president was obstructing justice by replacing Sessions with acting attorney general Matthew Whitaker, who immediately assumed control over special counsel Robert Mueller III’s investigation into Russian interference in the 2016 election. The inquiry had previously been overseen by Deputy Attorney General Rod Rosenstein.

Democrats indicated that the firing of Sessions would be one of their top investigation targets – and warned of a constitutional crisis. Rep. Adam Schiff, D-Calif., who is set to take over as chairman of the House Intelligence Committee, said in a statement that the Mueller probe was in “new and immediate peril.”

“Interference with the special counsel’s investigation would cause a constitutional crisis and undermine the rule of law,” Schiff said. “If the president seeks to interfere in the impartial administration of justice, the Congress must stop him. No one is above the law.”