One of the Senate's strongest voices will be quieter this week following Sen. John McCain's (R-AZ) diagnosis with brain cancer.
The six-term Arizona Republican was in his home state recently having surgery to remove a blood clot from above his eye when doctors found a brain tumor.
McCain, 80, received an outpouring of support and well wishes from his colleagues in Washington on Thursday following news of his condition, with many saying they expected to see him back on Capitol Hill as soon as possible.
I have enormous respect for John McCain. He's a fighter and if anyone can beat this, it’s John.— Sen Dianne Feinstein (@SenFeinstein) July 20, 2017
McCain's absence could spell more trouble for the fate of the GOP's health care plan, which is already crumbling under a fragile vote count.
"It makes things politically a lot harder," said Michael Cohen, director of the political management program at George Washington University.
"They've got to get that extra vote and they were already having a hard time getting two votes. They've got to get three and it looks like they've already lost four, so the math doesn't really seem to work very well in their favor."
The Senate had already announced the vote on the health care bill would be delayed until McCain returned from the blood clot surgery. Now, the brain cancer diagnosis could impact the bill even further.
"There's probably a bubble of time now where there's probably no outcomes coming out of the Senate," Cohen said.
Even President Trump, who has sparred with McCain in the media, admitted to reporters earlier this week that the Senate needs McCain at this crucial point in the health care battle.
"He's a crusty voice in Washington, plus we need his vote," Trump said during a speech in the White House on Monday.
McCain has said he's eager to get back to work as soon as possible to continue hammering out a solution on health care and to pass a defense spending bill.
But his glioblastoma diagnosis is a serious one and doctors say the average survival rate, with treatment, is about 14 months.
It's the same type of cancer that led to the deaths of former Sen. Ted Kennedy (D-MA) and Beau Biden, former Vice President Joe Biden's son.
Experts say if McCain leaves his Senate seat early, it could reshape the balance of the upper chamber.
McCain is known for challenging his Republican colleagues and working with lawmakers across the aisle to craft balanced legislation.
"Absent John McCain in the United States Senate, you end up with somebody who's probably more of a garden variety Republican and you end up with legislation that probably goes through a lot quicker, but you don't end up with a centrist piece of legislation or at least something that's closer to the center," Cohen said.
"I don't see another person in that seat making the same kinds of choices and holding the same kinds of conversations. John McCain is a unique person in American politics."
I greatly appreciate the outpouring of support - unfortunately for my sparring partners in Congress, I'll be back soon, so stand-by!— John McCain (@SenJohnMcCain) July 20, 2017
McCain's colleagues say that the former Navy pilot who was held captive in Vietnam for over five years is not one to give up easily and they don't expect him to give in to the disease without a fight.
"This disease has never had a more worthy opponent," said Sen. Lindsey Graham (R-SC), one of McCain's closest friends in the Senate.