WASHINGTON (AP) — President Donald Trump defended his firing of FBI Director James Comey, asserting in a flurry of tweets Wednesday that Republicans and Democrats "will be thanking me." Trump did not mention any effect the firing might have on the probe into contacts between his 2016 campaign and Russia.

Instead, Trump tweeted that he'll name a replacement "who will do a far better job, bringing back the spirit and prestige of the FBI."

Nevertheless, Tuesday's abrupt firing throws into question the future of the investigation into the Trump campaign's possible connections to Russia and immediately raised suspicions of an underhanded effort to stymie a probe that has shadowed the administration from the outset. Trump has ridiculed the investigations as "a hoax" and denied any campaign involvement with the Russians.

Democrats likened Comey's ouster to President Richard Nixon's "Saturday Night Massacre" and renewed calls for the appointment of a special prosecutor, and some Republicans also questioned the move.

In a flurry of tweets, Trump said Comey had "lost the confidence of almost everyone in Washington," adding: "When things calm down, they will be thanking me!"

In his brief letter Tuesday to Comey, Trump said the firing was necessary to restore "public trust and confidence" in the FBI. The administration paired the letter with a scathing review by Deputy Attorney General Rod Rosenstein of how Comey handled the investigation into Democrat Hillary Clinton's email practices, including his decision to hold a news conference announcing its findings and releasing "derogatory information" about Clinton.

While Comey has drawn anger from Democrats since he reopened the email investigation in the closing days of last year's campaign, they didn't buy that justification for his firing. Several Republicans joined them in raising alarms of how it could affect probes into possible coordination between Trump associates and Russia to influence the 2016 presidential election.

In one of the strongest statements by Republicans, Sen. Richard Burr of North Carolina, chairman of the Senate intelligence committee, said, "I am troubled by the timing and reasoning of Director Comey's termination."

"His dismissal further confuses an already difficult investigation by the committee," Burr said.

Senate Democratic Leader Chuck Schumer told Trump in a phone call he thought dumping Comey was a mistake. On Wednesday, Trump labeled the Senate minority leader "'Cryin' Chuck Schumer.'"

Trump will now appoint a successor at the FBI, which has been investigating since late July, and who will almost certainly have an impact on how the investigation moves forward and whether the public will accept its outcome.

It was only the second firing of an FBI director in history. President Bill Clinton dismissed William Sessions amid allegations of ethical lapses in 1993.

Democrats compared the ouster to Nixon's decision to fire the independent special prosecutor overseeing the Watergate investigation in 1973, which prompted the resignations of the Justice Department's top two officials.

"This is Nixonian," Sen. Bob Casey, D-Pa., declared on Twitter. "Outrageous," said Oregon Sen. Ron Wyden, calling for Comey to immediately be summoned to testify to Congress about the status of the Trump-Russia investigation. Rep. Adam Schiff of California, top Democrat on the House intelligence committee, said the White House was "brazenly interfering" in the probe.

Republican Sen. John McCain of Arizona said Congress must form a special committee to investigate Russia's interference in the election.

Senate Majority Leader Mitch McConnell, R-Ky., said only: "Once the Senate receives a nomination, we look forward to a full, fair and timely confirmation process to fill the director position. This is a critical role that is especially important as America faces serious threats at home and abroad."

Comey was speaking to agents at the FBI's field office in Los Angeles when the news broke. Television screens in the office began flashing the news, and Comey initially chuckled, according to a law enforcement official who was present and spoke on condition of anonymity. But Comey finished his speech before heading into an office and did not reappear in the main room. He later left Los Angeles on a plane to return to Washington.

In his letter to Comey, Trump thanked him for telling him three times "that I am not under investigation." The FBI has not confirmed that Comey ever made those assurances to the president. In public hearings, Comey has declined to answer when asked if Trump is under investigation, urging lawmakers not to read anything into that statement.

Comey, 56, was nominated by President Barack Obama for the FBI post in 2013 to a 10-year term, though that appointment does not ensure a director will serve the full term.

Praised frequently by both parties for his independence and integrity, he spent three decades in law enforcement. Before the past months' controversies, the former deputy attorney general in the George W. Bush administration was perhaps best known for a remarkable 2004 standoff with top officials over a federal domestic surveillance program. In March of that year, Comey rushed to the hospital bed of Attorney General John Ashcroft to physically stop White House officials in their bid to get his ailing boss to reauthorize a secret no-warrant wiretapping program.

But his prominent role in the 2016 presidential campaign raised questions about his judgment and impartiality. Though the FBI did not recommend charges against Clinton for mishandling classified information, Comey was blisteringly critical of her decision to use a personal email account and private internet server during her four years as secretary of state.

Comey strongly defended his decisions during a Senate Judiciary Committee hearing last week. He said he was "mildly nauseous" at the thought of having swayed the election but also said he would do the same again.

Clinton has partially blamed her loss on Comey's disclosure to Congress less than two weeks before Election Day that the email investigation would be revisited. Comey later said the FBI, again, had found no reason to bring any charges.

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AP writers Darlene Superville, Ken Thomas, Vivian Salama, Catherine Lucey and Sadie Gurman in Washington and Michael Balsamo in Los Angeles contributed to this report.