Sens. Joe Manchin, a Democrat from West Virginia, at left, speaks with Sen. Lisa Murkowski, a Republican from Alaska, during a hearing on Capitol Hill in Washington, in July 2021.
CNN  — 

Two key moderate senators – Democratic Sen. Joe Manchin of West Virginia and Republican Sen. Lisa Murkowski of Alaska – announced Monday that they have tested positive for Covid-19.

“This morning I tested positive for COVID-19,” Manchin tweeted. “I am fully vaccinated and boosted and am experiencing mild symptoms. I will isolate and follow CDC guidelines as I continue to work remotely to serve West Virginians.”

Several hours later, Murkowski tweeted, “After experiencing flu like symptoms I recently tested positive for COVID-19. I will be following guidance and advice from doctors and will be quarantining at home in Alaska while continuing my work remotely.”

It’s unclear what effect, if any, Manchin’s isolation will have on Democrats’ efforts to make progress on their legislative agenda. The Senate has a little under two weeks before it’s scheduled to start its August recess, and Democrats have indicated hopes in passing bills – from protecting same-sex marriage to increasing funding for semiconductor production in the US and changing laws surrounding prescription drug prices among other issues – before leaving town for about a month.

As one of the most moderate Democrats in Congress, Manchin represents an important vote in the Senate that is split 50-50, and his support is necessary for most legislation that is divided along partisan lines. Perhaps most notably, Manchin has been a key negotiator in a package to overhaul Medicare prescription drug prices and extend health care subsidies for Affordable Care Act coverage.

While Republicans are in the minority in the chamber, Murkowski has been supportive of the legislation protecting same-sex marriage, a bill for which at least 10 GOP senators would need to back with all 50 Democrats in order to overcome a filibuster.

While Manchin and Murkowski can continue to work remotely, Senate floor votes must take place in person. The chamber does not have a proxy voting system for floor votes like the House of Representatives adopted at the start of the Covid-19 pandemic.

Manchin is just the latest Washington lawmaker sidelined from Capitol Hill due to Covid. Senate Majority Leader Chuck Schumer tested positive and had to isolate earlier this month, as did a handful of others. Democratic Sens. Tom Carper of Delaware and Tina Smith of Minnesota both announced last week they had tested positive, as did President Joe Biden.

Biden’s physician said Monday that the President’s symptoms have “almost completely resolved.” He is isolating at the White House.

And Covid-19 isn’t the only medical issue affecting the Democrats’ numbers in the chamber this summer. Vermont Sen. Patrick Leahy has been recuperating from a broken hip in June, rehabilitation which included surgery as recently as last week. Leahy’s office has said the senator would be available for votes if needed.

This story and headline have been updated with additional developments Monday.