The Mood in the Capitol Was Already Dark. Then Came Omicron.

WASHINGTON — Across the country, the Omicron variant has sent coronavirus infections into the stratosphere. Winter weather and empty shelves have turned moods surly. Americans have turned on each other over vaccinations, mandates and masks.

And at the U.S. Capitol, where all manner of people are thrown together in an unhappy stew, the moment was crystallized this week in a hot-mic episode. In an audible whisper, Dr. Anthony S. Fauci, the government’s top infectious disease expert, summed up his feelings for another physician, Senator Roger Marshall, Republican of Kansas.

“What a moron,” Dr. Fauci said on Tuesday after a testy exchange with the senator over the infectious disease expert’s financial disclosures. “Jesus Christ.”

Just when it seemed as if the atmosphere on Capitol Hill could not get worse, Omicron came to town. At least 129 House members and senators have announced a coronavirus infection since the outset of the pandemic, nearly a quarter of the lawmakers in Congress. A baker’s dozen announced infections in the last week alone. A mask mandate that has been only fitfully respected by Republicans in the House was turned up a notch to require only N95s and KN95s — and compliance is just as spotty.

Social distancing is back; when the body of Harry Reid, the former Senate majority leader, lay in state in the Capitol Rotunda on Wednesday, chairs were arranged several feet apart. The grand atrium of the Capitol Visitor Center, once filled with tourists, has been reconfigured with stanchions to demarcate the Covid testing line for lawmakers and staff members.

Schadenfreude is in full tilt.

Democrats cackled about what Dr. Fauci called Mr. Marshall; Republicans countered by invoking Representative Alexandria Ocasio-Cortez, Democrat of New York, who was spotted maskless in Miami Beach late last month. Her office announced on Sunday that she had tested positive for the virus.

Of course, it is no laughing matter. Two Republicans have died after contracting Covid — Representative Ron Wright of Texas and Representative-elect Luke Letlow of Louisiana — and the refusal of some lawmakers on the right fringe to wear a mask in the hustle and bustle of House floor votes has some colleagues fearing for their health.

“I see people — members, staff — without masks,” the House sergeant-at-arms, William J. Walker, a former District of Columbia National Guard commander, said this week. “I’ll walk up to them and ask them to put the mask on. Some just walk away from me.”

On the House floor on Wednesday, Representative Brian Mast, Republican of Florida, walked through the well on two prosthetic legs, smiling broadly without his mask. In the back of the chamber, Georgia’s maskless duo, Representatives Marjorie Taylor Greene and Andrew Clyde, both Republicans, held court seemingly without a care, sure to get fined for their rule-breaking but confident their fortunes could handle it.

(Ms. Greene’s father built a significant Atlanta-area building company before selling it to his daughter and son-in-law, while Mr. Clyde’s hulking gun shop, Clyde Armory, has kept him flush. They have already absorbed more than $100,000 in fines for their mask strike.)

Speaking just outside the chamber with his mask off, Representative Lee Zeldin, Republican of New York, was nonchalant. Omicron is mild, he said, and the steep rise in cases, in his home county on Long Island and across the country, will be followed by an equally steep decline.

“Those who are testing positive include the vaccinated and the unvaccinated, but for those I speak to — and there are many who have tested positive in recent weeks — fortunately for them, every single person I’ve spoken to has had a much milder experience than what was experienced in past variants,” said Mr. Zeldin, who is running for governor of New York.

Democrats tend to be a little less sanguine. Signs posted throughout the House proclaim in all capital letters “USE OF FACE COVERINGS REQUIRED,” but they appear to have only made the defiant dig in.

“That kind of defiance, we see it all across the board here,” said Representative James E. Clyburn of South Carolina, the Democratic whip, who missed his granddaughter’s wedding last month as he battled Covid. “And these are people who I hope will be able to survive whatever comes their way.”

The procedural machinations around voting rights legislation and the hand-wringing over President Biden’s social safety net and climate change bill can seem a bit beside the point when cases are soaring, hospitalizations nationwide are up 84 percent over the past two weeks and the average number of deaths now exceeds 1,700 a day.

Behind those marquee issues, the pandemic is again rising as a political focus. House Democrats on Wednesday rushed out new legislation to provide free at-home coronavirus tests while Senator Bernie Sanders, independent of Vermont, reintroduced his bill to send N95 masks to every home.

For their part, Republicans appeared to have determined that the real victims of the virus were those who refused to be vaccinated against it.

House Republican leaders forced Democrats to vote on a procedural motion to ensure that service members discharged for refusing to be vaccinated would not lose their G.I. Bill benefits. It failed.

Representative Matt Gaetz, Republican of Florida, and 19 other House members on the party’s right flank also introduced a bill to block the District of Columbia from requiring vaccinations to enter establishments like restaurants, clubs and concert venues.

The conflict that erupted this week between Dr. Fauci and Mr. Marshall was over a serious issue, as was a clash between the infectious disease expert and Senator Rand Paul, Republican of Kentucky.

Mr. Paul, an ophthalmologist, accused Dr. Fauci and the director of the National Institutes of Health, Dr. Francis S. Collins, of collaborating to smear scientists who disagreed with them. That prompted Dr. Fauci to recount the arrest of a California man who was driving across the country with an AR-15; the man was accused of planning to kill Dr. Fauci, among other public figures.

And though Dr. Fauci could easily parry Mr. Marshall’s insinuation that he was somehow hiding his financial disclosure records, few could argue with the senator’s assertion that government messages have been mixed and confusing on quarantine lengths and testing during the Omicron surge.

“The American people, my family, all of our families, are struggling as this pandemic continues to drag on with no end in sight,” Mr. Marshall said during a sparsely attended hearing, depleted of participants and observers because of Covid’s resurgence. “The words I hear every day, multiple times each day, continue to resonate and echo in my mind, words like, ‘I’m tired, confused, burned out.’”

Representative Tom Cole, Republican of Oklahoma, agreed on Wednesday that the mood in the Capitol reflected the mood at home.

“Obviously it’s a very difficult time,” he said. “We all thought we’d be on top of the virus now. We’re clearly not.”

He added: “We’ll get through it. The country’s seen a lot darker days than these.”

Luke Broadwater contributed reporting.