In recent months, the members of Congress who have publicly reported coronavirus cases overwhelmingly have been Democrats — including the party’s two top leaders on Capitol Hill — posing a big and ironic problem for the majority party.

By testing more frequently than their Republican colleagues, Democrats are facing the possibility that their strict adherence to public health protocols could backfire as they pursue the passage of major domestic policy legislation through the 50-50 Senate in the coming weeks.

The stakes were placed into stark relief after Senate Majority Leader Charles E. Schumer (D-N.Y.) and Sen. Richard Blumenthal (D-Conn.) reported positive tests, making them unable to vote this week. While their absence has not affected this week’s Senate agenda, and both senators have continued to work while isolated, any future Democratic absences could upend plans to pass the party-line economic package that is now under negotiation between Schumer, Sen. Joe Manchin III (D-W.Va.) and other Democrats.

Lawmakers of both parties agree that Democrats appear to be victims of their own diligence, testing more frequently than Republicans and publicizing their results more routinely.

“We need every Democrat,” said Sen. Tim Kaine (D-Va.), who added that he was doubtful of an actual partisan disparity in viral incidence: “I would venture to suggest that the rates of infection are precisely identical between Democrats and Republicans. One group is publicly disclosing, and one group is not — that is my intuition.”

“Either they’re not telling us or they’re simply not getting tested,” said Sen. Mazie Hirono (D-Hawaii).

According to GovTrack.us, a nonpartisan data clearinghouse that tracks members’ coronavirus disclosures, 65 members of Congress have publicly reported positive tests and isolated themselves since the beginning of March, when the omicron wave subsided. The tally does not include Blumenthal’s test, which he disclosed Monday.

Only five of those 66 lawmakers — about 8 percent — are Republicans.

Multiple Republican lawmakers interviewed this week did not dispute Kaine’s theory, with nearly all of them conceding that Democrats probably test more frequently for various reasons.

“We’re probably not reporting our results or offering as many tests,” said Sen. Mitt Romney (R-Utah), who tested positive in January at the height of the omicron wave.

Some Republicans, in fact, suggested that Democrats are simply testing too much.

“We’re in an endemic now, not a pandemic, and I guess you can continue that [testing] protocol as far into the future as you want to,” Sen. Mike Braun (R-Ind.) said. But he added that “sometimes your policies can get to be very inconvenient when they don’t make sense.”

Others were outright flippant: Sen. Bill Cassidy (R-La.), a physician, joked that the Democrats’ dilemma was a matter of “karma.”

“When you’re trying to put forward bad bills, you get attendance problems,” he said.

In the House, positive tests have scant political consequences. In the early months of the pandemic, the chamber instituted proxy voting, which allows a member to designate a colleague to cast floor votes on his of her behalf. In April, House Speaker Nancy Pelosi (D-Calif.) announced that she tested positive for the coronavirus.

The Senate, however, does not allow proxy voting, and the margins are tighter — Vice President Harris’s tiebreaking vote is all that guarantees Democrats’ majority in a Senate that has been evenly split between the parties since January 2021.

The chamber has had full attendance for only a handful of votes this year. While GOP absences have frequently allowed Democrats to move some controversial measures without full attendance — such as Tuesday’s confirmation of former federal prosecutor Steve Dettelbach as Bureau of Alcohol, Tobacco, Firearms and Explosives director — some other key votes have been delayed or abandoned due to Democratic absences.

But the possible consideration of a party-line economic package — a modified revival of the Build Back Better domestic policy bill that foundered last year due to Democratic infighting — stands to be a razor’s edge affair even without the threat of a new coronavirus variant bearing down on the Capitol.

Under Senate rules, moving the package across the chamber wouldn’t simply be a matter of a couple of votes, it would be a weeks-long process of negotiation culminating in a “vote-a-rama,” a marathon series of amendment votes likely to stretch through the night into the following morning.

Already there are non-covid-related absences that have given Democrats reasons to fret: Sen. Patrick J. Leahy (D-Vt.) underwent hip replacement surgery last month and has yet to return to vote, and two other Democratic senators, Ben Ray Luján (N.M.) and Chris Van Hollen (Md.), suffered minor strokes that caused them to miss votes earlier this year.

One key factor in the testing disparity between the two parties: Although Congress itself has no set testing protocol, the White House does, and many lawmakers have reported positive tests after being screened for meetings with President Biden or Harris. By and large, those meetings tend to involve congressional Democrats, not Republicans.

Schumer and Blumenthal, for instance, reported their positive tests this week just ahead of a Monday event on the South Lawn commemorating the recent passage of bipartisan gun violence legislation. On Tuesday, Biden hosted the annual congressional picnic — an event that drew a largely but not exclusively Democratic crowd.

For Republicans, meanwhile, testing practices appear to be spottier, and largely depend on the whims and schedules of individual lawmakers. Sen. Roger Wicker (R-Miss.), the last Republican lawmaker to disclose a positive test, said he took a test to attend an event.

“I test when I’m asked to test,” said Sen. Mike Rounds (R-S.D.). “I wouldn’t be afraid to test if I had symptoms. But I’m not having symptoms, I’m not going out of my way to test.”

Sen. Kevin Cramer (R-N.D.) said he has not taken a coronavirus test since January 2021, when one was required to attend was Biden’s inauguration. He said he has not experienced any symptoms since the pandemic began, and “I never took a test out of curiosity.”

Cramer said he has declined invitations to the White House since then, in part, because of the testing and masking requirements.

“The problem with testing positive at the White House is, other people know you tested positive as opposed to doing it in your own bedroom,” he said,explaining why he believed Democrats were reporting more cases.

Earlier in the pandemic, Democrats and Republicans could be discerned simply through their mask-wearing habits, but things are now less clear-cut.

On Capitol Hill this week, the vast majority of senators went maskless, though a handful of Democrats still wear them faithfully. Lines at the Senate testing center, which often featured hour-long waits during covid waves, are now largely nonexistent.

Sen. Richard J. Durbin (D-Ill.), who is in charge of corralling Democratic votes as majority whip, explained the partisan disparity by pointing to Democrats’ frequent White House visits. But he demurred when asked whether Democrats would be wise to take more precautions — and perhaps stop visiting the White House — should the economic talks advance.

But other senators and aides are quietly starting to wonder whether more precautions are warranted, given the stakes for both health and policy. Some have discussed encouraging more mask-wearing and substituting Zoom meetings for in-person gatherings.

“The whole country is depending on us, so we need to stay healthy,” said Sen. Brian Schatz (D-Hawaii). “As we get closer to go-time, we should be increasingly careful.”