WASHINGTON — The sense of crisis enveloping President Trump’s White House generated growing frustrations Wednesday as congressional Democrats redoubled demands for tough investigations of the new administration’s ties to Russia and congressional ­Republicans found themselves on the defensive.

Tensions on Capitol Hill — already high after national security adviser Michael Flynn’s forced resignation Monday night — rose even higher following press reports of Flynn’s contacts with Russia’s ambassador to the United States. Related accounts emerged Tuesday of even more widespread contact between Trump campaign figures and Russia during the 2016 campaign.

In another blow Wednesday, Trump’s nominee for secretary of the Labor Department withdrew amid allegations of domestic violence and questions about his employment of an undocumented housecleaner.

Republicans are growing worried that the day-after-day controversies emanating from the White House and Trump’s Twitter feed are dragging down momentum for a big conservative agenda made possible by GOP control of the White House and both chambers of Congress. Republicans started the year with lofty hopes of overhauling the tax code, making good on years of promises to repeal the Affordable Care Act, and slashing scores of other Obama-era ­regulations.

“There are things that we want to get done here. We want to have a clear-eyed focus on our agenda, and this constant disruption and drumbeat with these questions that keep getting raised is a distraction. There’s no way around it,’’ said South Dakota’s John Thune, the third-ranking member of Senate GOP leadership. He urged the White House to cooperate with congressional committees in answering the mounting questions about contacts between Trump’s associates and Russia.

His advice to the White House: “Get it all out there and put it behind you and let’s move forward.’’

“It’s time to get past the launch phase,’’ he added.

Despite the frustration in the GOP ranks, Republicans continued to resist the growing chorus of Democrats calling to elevate the probe into the ­Russia controversy beyond the normal committee structure by appointing a special prosecutor or independent investigating committee. For now, the lead role in the inquiry is being taken by the Senate Intelligence Committee, whose leaders have indicated it is expanding an existing probe into Russian meddling in the 2016 presidential election to include Flynn’s activities.

“I don’t think we need a ­select committee. We know how to do our work. We have an Intelligence Committee,’’ ­Senate majority leader Mitch McConnell said in an interview with MSNBC that aired Wednesday morning.

Thune and other Republican senators echoed that view Wednesday: “Let’s let our committees do their jobs and see where that takes us,’’ Thune said. “That process does need to move forward.’’

Still, the tenor of GOP comments was hardening in terms of the need for a vigorous probe on the latest revelations.

“I can’t say with confidence on anything except that this is a serious issue and has to be addressed,’’ said GOP Senator John McCain of Arizona, when asked whether he felt confident President Trump was not involved in directing Flynn to discuss sanctions with Russia.

“The president’s national security adviser did not tell the vice president of the United States the truth and had to be fired,’’ McCain said. “That brings up a lot of questions, and those questions need to be answered.’’

McCain said the chaos in the White House has left the country “dysfunctional’’ when it comes to national security, putting the United States at risk.

As for the GOP agenda, ­McCain said, “Something like this always sucks the oxygen out of the room.’’

Other Republicans were defensive, saying the real obstacle to their legislative hopes were recalcitrant Democrats who were unfairly trying to deny Trump a full Cabinet. Still, several of them agreed with Democrats that Flynn needed to come to the Hill and testify. And frustration could be read between the lines of their talking points when the topic turned back to Russia.

“I think I talked about that all day yesterday,’’ said Senator Roy Blunt, a Missouri Republican and member of the Intelligence Committee, when asked about the latest revelations on the Trump campaign’s interactions with Russia.

“There’s a cloud over the White House when it comes to Russian matters,’’ South Carolina Senator Lindsey Graham said, quickly pivoting from blaming Democrats for blockading Trump’s Cabinet.

“I would urge the president to seize a leadership role and say, ‘If there’s something out there, I want to know it as much as everyone else; if somebody on my campaign did something wrong, I want to know about it,’ ’’ he said. “That would help us move forward.’’

Graham said while it would have been inappropriate for Trump, as president-elect, to have directed Flynn to discuss sanctions with the Russians during the transition, it would not be illegal. Contacts during the campaign, however, could be a much bigger deal, he said.

“If there are contacts between the Trump campaign and Russian intelligence officers outside the norm, that takes this whole issue in a dramatically different area. That would open up an investigation of everything Trump related to Russia,’’ Graham said. “The way you fix this is for the president himself basically to work with the Congress in a bipartisan fashion to look into what happened and to let the facts speaks for themselves.’’

Senate Democrats held an emergency caucus meeting Wednesday to discuss how they should handle the growing controversy.

Senators emerged to say that, for now, Democratic leaders were satisfied with the steps being taken by the Senate Intelligence Committee. That view was not unanimous among Democrats.

“We need an independent investigation. I am just not convinced that Mitch McConnell is going to let the Intelligence Committee get to the real story,’’ said Senator Chris Murphy, a Democrat from Connecticut. Murphy said his ideal situation would be for a 9/11-type independent commission to handle the investigation. Other senators said a special prosector should be appointed.

Democrats did issue a united call for Attorney General Jeff Sessions to recuse himself from any investigations into ties between Trump’s aides and Russia because they don’t believe the former Alabama senator can be impartial toward a president for whom he vigorously campaigned.

“If this trail leads to the Oval Office, the person investigating that trail should not be the same person who helped put President Trump there,’’ Senate Minority Leader Chuck Schumer said.

Schumer also said Democrats want all records pertinent to the investigation to be preserved and all implicated members of Trump’s campaign to publicly testify before Senate committees.

“I’ve been in Congress for a long time. I’ve never seen anything like this,’’ Schumer said. “We are Americans before we are Democrats and Republicans. Nothing less than our system of checks and balances, democratic institutions, rule of law, and our national security is at stake.’’

Victoria McGrane can be reached at victoria.mcgrane@globe.com. Follow her on Twitter @vgmac.