The furor over President Trump’s abrupt firing of FBI Director James B. Comey grew Wednesday with the revelation that Comey had sought more resources for an investigation into possible coordination between the Trump campaign and the Russian government shortly before he was dismissed.

Republicans and Democrats alike expressed dismay Wednesday over Comey’s firing the day before, which several said will frustrate bipartisan efforts to investigate Russian interference in the 2016 election and any possible ties between the Kremlin and Trump associates. Many Democrats called for a special prosecutor to take on the investigation, and a handful of Republicans said they were open to the idea.

For some, the news of the request provided further evidence that Trump’s stated reason for firing Comey — that the director had botched the bureau’s investigation of Hillary Clinton’s private email server — was untrue. The likelier and more troubling reason, critics said, was to quash the Russia investigation and the threat it poses to the Trump White House.

“This really smacks of impropriety,” said Sen. Jon Tester (D-Mont.), who said he believes the president is “using Hillary and the server as an excuse to say, ‘We’re getting rid of this guy because he’s getting too close to us.’ ”

Although several Democrats confirmed that Comey had informed lawmakers of the request he made last week in a meeting with Deputy Attorney General Rod J. Rosenstein, the Justice Department denied those reports.

Several influential Republicans, including Sens. John McCain (Ariz.) and Bob Corker (Tenn.), declined to say whether they accepted the reasons given for Comey’s firing, which were laid out in a memo written by Rosenstein.

But Senate Majority Leader Mitch McConnell (R-Ky.) dismissed concerns and rapped Democrats for complaining about the ouster of an FBI director they had “repeatedly and sharply criticized.” McConnell also made clear his plans for the coming days: to keep the chamber’s focus on the GOP’s policy agenda, including passage of a health-care overhaul and tax reform.

Others were more pessimistic that the emergence of yet another Trump-related controversy would slow the Senate’s work. Comey’s firing is expected to consume Capitol Hill’s attention until the weekend and potentially through Tuesday, when the former FBI director has been invited to testify before the Senate Intelligence Committee.

The panel’s chairman, who met with Comey on Monday, said the director’s dismissal makes the committee’s work harder.

[President Trump fires FBI Director Comey]

“It creates challenges for the committee,” Sen. Richard Burr (R-N.C.) told reporters. “An interruption in any of the access we have to the documents or the personnel would be harmful to our investigation.”

The chairman of the House Oversight and Government Reform Committee, Rep. Jason Chaffetz (R-Utah), sent a letter Wednesday to Justice Department Inspector General Michael Horowitz asking him to look into the Comey firing.

(Elyse Samuels/The Washington Post)

Also Wednesday, the Senate Intelligence Committee issued a subpoena for documents related to former national security adviser Michael Flynn and his ties to Russia. In an announcement, Burr and the ranking Democratic member, Sen. Mark R. Warner (Va.), said Flynn had declined to cooperate with their first request.

Burr and Warner met Monday with Comey, according to several individuals familiar with the meeting. Later, at a regular meeting of Democrats on the Senate Intelligence Committee, Warner informed them that Comey had briefed the two committee chiefs about his request for more resources, according to two officials, who were not authorized to speak publicly about the matter.

Adding to the drama Wednesday was Russian Foreign Minister Sergei Lavrov’s visit to Washington — including a closed event at the White House that U.S. news organizations were barred from witnessing even though a photographer from the state-run Russian news service Tass was permitted.

Lavrov fended off questions about Russian interference in the presidential election. And during a visit with Secretary of State Rex Tillerson, Lavrov professed mock surprise when asked whether Comey’s firing had cast a shadow over his visit.

“Was he fired?” Lavrov said, arching his eyebrows. “You’re kidding! You’re kidding!”

Capitol Hill Democrats and a few Republicans, meanwhile, demanded the launch of an independent investigation into Russia’s interference in the election. To increase pressure, Senate Democrats invoked an obscure rule that prevented committee hearings from continuing past midday.

Senate Minority Leader Charles E. Schumer (D-N.Y.) said the Justice Department’s highest-ranking career civil servant, rather than Rosenstein, should appoint a special prosecutor to lead the Russia investigation.

A Trump appointee who assumed office just 10 days ago, Rosenstein wrote the memo that was used to justify Comey’s firing. The document, issued Tuesday, laid out the director’s missteps in handling the FBI investigation into Hillary Clinton’s private email server.

Schumer also called for both Rosenstein and Attorney General Jeff Sessions to brief the entire Senate on the events that led to Comey’s firing — and he urged Comey to accept the invitation to testify next week.

Comey was scheduled to testify Thursday before the Intelligence Committee about national security threats to the United States. Acting FBI director Andrew McCabe is set to appear in his place, along with a slew of other security and intelligence officials.

[Comey’s removal sparks fears about future of Russia probe]

“There are so many unanswered questions that only Mr. Comey can answer. We Democrats hope and expect that he will still come before the Senate in some capacity,” Schumer said.

To press for the special prosecutor, Senate Democrats may also try to slow down the process of confirming lower-level nominees. Such a move would probably hamper executive-branch agencies that now lack political leadership, including dozens already in the confirmation pipeline.

Sen. Ron Wyden (D-Ore.) took a step down that path Wednesday, when he said he was putting a hold on Sigal Mandelker, Trump’s nominee to a key Treasury Department post. Wyden said he would maintain the hold until the agency provides lawmakers with more documents related to Russia and its dealings with Trump and his associates. However, the procedural tactic can be easily overridden.

Some Democrats said they wanted to give Republicans time to form their own response before deciding on the next steps.

Sen. Claire McCaskill (D-Mo.) recommended that Democrats reach out to Republicans, noting that a small but powerful bloc of GOP senators has voiced concerns about the Comey firing.

Sen. Chris Murphy (D-Conn.) agreed: “This is 12 hours old. I think we have to give a little time for Republicans to have a conversation and perhaps rise to the occasion.”

Among Senate Republicans, only McCain, a longtime Trump foil, has called for an independent investigation separate from ongoing probes by the House and Senate intelligence panels.

Other members of the GOP cast doubt on the decision to fire Comey but remained circumspect about the idea of a special prosecutor.

“Let us finish our work,” Burr said. “It’s moving forward. We’re finally making some significant progress. Let us issue a report.”

“I do have questions about why he was dismissed at this time,” said Sen. Marco Rubio (R-Fla.), a member of the Intelligence Committee.

“[But] if you were to appoint a special prosecutor today on that or any issue,” he added, “it would probably shut down our ability to do our work, because a significant amount of information would now be denied.”

Corker, the chairman of the Senate Foreign Relations Committee, called on Trump to appoint an FBI director who is “beyond reproach.”

“I think the White House, after multiple conversations with many people over the last 12 to 14 hours, understand that they created a really difficult situation for themselves,” he said. “To move beyond this in a way that gives the American people faith and Republicans and Democrats in the House and Senate faith in future efforts is going to be a really tough and narrow path for them to follow.”

House lawmakers, away on a week-long recess, were not in Washington on Wednesday. House Speaker Paul D. Ryan (R-Wis.) shot down the idea of a special prosecutor during an evening interview with Fox News.

“I don’t think that’s a good idea,” he said. “The intelligence committees are the ones that should do this. . . . Let’s see them through. Let’s see where the facts may lead.”

Ryan did not express a personal view of Comey’s firing.

“He had basically lost the confidence of a lot of Republicans and a lot of Democrats,” Ryan said. “It is entirely within the president’s role and authority to relieve him and that’s what he did.”

Some Republicans tried to steer the conversation away from the topic of Russia throughout the day.

During a visit to Capitol Hill, Vice President Pence repeated Trump’s claim that Comey informed him several times that he was “not under investigation.” The White House has not substantiated that claim.

“The simple fact is, Director Comey had lost the confidence of the American people,” Pence said, defending Trump’s decision.

Senate Republican Whip John Cornyn (Tex.) dismissed the notion that Trump fired Comey to impede the FBI’s Russia probe, calling it a “phony narrative.”

“If you assume that, this strikes me as a lousy way to do it,” he told reporters. “All it does is heighten the attention given to the issue.”

[The shocking firing of James B. Comey puts new pressure on Trump and his team]

While Democrats discussed strategy, Republicans were trying to move on — a sign of how unwelcome these developments are for their agenda.

At a Wednesday lunch attended by Senate Republicans, Comey barely came up in the group discussion, according to attendees.

“We were focused on health care and there might have been 120 seconds devoted to it,” Corker said.

“No talk when I was there,” Sen. Jeff Flake (R-Ariz.) said.

Karoun Demirjian, Kelsey Snell, Tom Hamburger, James Hohmann and Ashley Parker contributed to this report.