Mask mandates returned to the House and the White House, while the Senate was strongly encouraged to use high-quality face coverings as well to help slow down the delta variant of COVID-19.

Attending Physician Brian Monahan’s messages to the House and Senate made the same substantive point, that the new guidance this week from the Centers for Disease Control and Prevention regarding indoor mask use by fully vaccinated individuals in areas where the virus is spreading has led him to recommend that Congress follow suit.

“For the Congress, representing a collection of individuals traveling weekly from various risk areas (both high and low rates of disease transmission), all individuals should wear a well-fitted, medical-grade filtration mask (for example an ear loop surgical mask or a KN95 mask) when they are in an interior space and other individuals are present,” Monahan wrote late Tuesday in a letter to Senate Majority Leader Charles E. Schumer and Minority Leader Mitch McConnell.

The message to the House went further, reinstating requirements for wearing face masks in the hall of the House, the House office buildings and committee meetings when in the presence of other people.

On Wednesday morning, Speaker Nancy Pelosi announced that masks were again required in the halls of the House but that members were permitted to temporarily remove them when recognized by the chair to speak. She also reminded members that the House sergeant-at-arms is authorized and directed to impose fines for violations of this policy.

Over at the White House, staff moved quickly on Tuesday to restore the mask requirements following the formal announcement by CDC Director Rochelle Walensky of the updated guidance. The guidance is based in part on new research suggesting that the viral load of the delta variant may be significant in vaccinated people — though the vaccines clearly provide protection against hospitalization and death.

More voluntary mask-wearing resumed Tuesday on Capitol Hill even before the messages from Monahan, but it may prove difficult to go back to the practice there. Some Republican senators openly questioned the wisdom of the new CDC guidance.

“Do masks even work? Do they do more harm than good — particularly to children who have a low risk of serious disease or death from Covid? Remember, the initial goal of public policy was to flatten the curve so we wouldn’t overwhelm hospitals,” Sen. Ron Johnson, R-Wis., said in a statement Tuesday night. “At some point, federal agencies moved the goal posts. The initial goal was achievable. I’m not even sure what the new goal is.”

All credible information indicates that high-quality masks, particularly N95 masks and similar coverings, are useful in reducing the risk of transmission of COVID-19.

In another sign of how the pandemic is still affecting the Capitol, a scheduled meeting of the Senate Homeland Security and Governmental Affairs Committee was postponed because of a possible COVID-19 exposure, a committee aide confirmed.

Walensky and Anthony Fauci, the chief medical adviser to President Joe Biden, will be asked about the new guidance when they brief members of the House’s Select Subcommittee on the Coronavirus Crisis, according to Chair James E. Clyburn, D-S.C.

“Today’s announcement underscores the fact that we already have the tools needed to protect Americans against this deadly virus: safe and effective vaccines. We must double down in our collective efforts to get more Americans vaccinated — to protect themselves, their families, and their communities. I urge all Americans 12 years of age and older who remain unvaccinated to get their vaccinations immediately, ” Clyburn said in a statement Tuesday. “Expeditiously reaching near-universal vaccination will significantly reduce the threat of the virus and will enable the CDC to revisit today’s guidance. Until that happens, I urge all Americans to follow these science-based recommendations.”

Later in the day, after House Republicans met with Monahan, House Minority Leader Kevin McCarthy came to the floor during debate on the fiscal 2022 Legislative Branch spending bill to question the science of the new requirements, saying the determination was based on a study out of India that involves a vaccine not used in the U.S.

“There is no science, but I guess the speaker must have not known that,” McCarthy said. “First they tell us don’t wear a mask, wear a mask, wear two masks, then they take the mask off. They said if Americans got vaccinated, we’d get our lives back, and we did,” the California Republican said, citing past cases in which California Democrats, including Pelosi, appeared to be out of compliance with the mask rules there. “I don’t know, the gentleman over there’s going to run for the Senate. Maybe he wants to do that so he doesn’t have to wear a mask,” McCarthy said of Legislative Branch Appropriations Subcommittee Chair Tim Ryan, D-Ohio. “The science over there is better,” he said, referring to the Senate’s lack of a mask mandate.

Ryan felt the need to respond.

“Look, the attending physician of the United States Capitol, the top doctor for Congress, asks us to put on masks when we come to a chamber with 435 people,” Ryan said in response. “Somebody in this chamber is coming from a hot spot. Somebody represents the hot spots,” and such vectors put families with young children and immunocompromised family members at unnecessary risk, he said.

“I just find it absolutely immature and appalling to somehow diminish it to try to score cheap political points,” Ryan said. “That is beneath a minority leader of one of the major political parties in the United States of America.”

Suzanne Monyak and Mark Burnett contributed to this report.