Applause and cheers greeted Senator John McCain, who is battling brain cancer, as he returned to the Capitol on Tuesday to vote for moving ahead on legislation to dismantle Obamacare.
The 80-year-old had a visible scar above his left eye after doctors removed a blood clot earlier this month.
Days after the surgery, the senator disclosed that he had a brain tumour and had been diagnosed with an aggressive form of cancer.
"Stop listening to the bombastic loudmouths on the radio, TV and internet. To hell with them!" the feisty Mr McCain said in a speech on the Senate floor.
He bemoaned the lack of legislative action in Congress.
Mr McCain also said he would not vote for the current Republican version of the repeal and replace bill.
He drew a standing ovation after his remarks.
Mr McCain had cast his vote to take up the healthcare bill, delivering for his party and President Donald Trump on the issue that has defined the party for the past seven years.
"He's tough as a boot," said Republican Senator John Kennedy. "Many people understandably would be curled up in bed in the foetal position."
Mr McCain himself campaigned heavily on the Obamacare repeal issue last year as he won re-election to a sixth and almost certainly final Senate term.
And there could be sweet revenge in defying cancer to undo the signature legislation of the man who beat him for the presidency in 2008, Barack Obama.
The Arizona senator would also deliver a key victory to Mr Trump, despite emerging as one of the president's most outspoken Republican critics on Capitol Hill.
During last year's campaign Mr Trump shockingly ridiculed Mr McCain over his years as a prisoner of war during the Vietnam War.
And the situation was eerily reminiscent of a similar scenario involving Mr McCain's good friend, the late Democratic Senator Ted Kennedy, who returned to the Senate in July 2008 while battling brain cancer to vote on Medicare legislation, his dramatic entry in the chamber eliciting cheers and applause.
Mr Kennedy died of cancer in August 2009 (the current Senator Kennedy is no relation).
The possibility of Mr McCain returning had been discussed around the Capitol on Monday, yet the announcement from his office late in the day came as a surprise.
Nor did it guarantee success on Tuesday's vote for Majority Leader Mitch McConnell, who is managing an awkward Republican caucus with almost no room for error in the closely divided Senate.
Yet fellow Republicans took Mr McCain's return as a positive sign for Tuesday's vote.
"John McCain's coming back. That's positive," said Senator Richard Burr.
Mr McCain has not been overly enthusiastic about the Republican health bill or the partisan process through which it has emerged.
After an earlier version was poised to fail, he called on Mr McConnell to reopen the process with a bipartisan approach, advice the majority leader ignored.
But Mr McCain's best friend in the Senate, Lindsey Graham, and other colleagues who have spoken with Mr McCain of late, say he has been itching to get back to the Senate, impatient to return to work.
"Is it surprising that he would get out of a hospital bed and go to work? No," Mr Graham said. "It's surprising he's been in the hospital this long."