WASHINGTON (AP) -- Arizona Sen. John McCain has discontinued medical treatment for an aggressive form of brain cancer, says his family.
It's a likely indication that the war hero, presidential nominee and longtime lawmaker is nearing the end of his life.
The 81-year-old McCain has surpassed expectations for survival, but "the progress of disease and the inexorable advance of age render their verdict," the family said. "With his usual strength of will, he has now chosen to discontinue medical treatment."
The six-term GOP senator, whose birthday is Aug. 29, has been away from the Capitol since last December.
If McCain should resign his seat or die soon, Republican Arizona Gov. Doug Ducey would name a replacement to serve until the 2020 election. The winner of that election would serve the remainder of McCain's term through 2022.
In more than three decades in Congress, McCain became known as a political maverick willing to stick to his convictions rather than go along with party leaders — an independent streak that has drawn a mix of respect and ire.
Most recently, he has been a thorn in the side of President Donald Trump, keeping up his criticism of the White House even while undergoing severe medical treatment in Arizona.
In July, he issued a searing rebuke of Trump's summit with Russian President Vladimir Putin, calling it a "tragic mistake" and "one of the most disgraceful performances by an American president in memory."
The strained relationship between Trump and McCain dates back to 2015, when Trump suggested the Vietnam veteran, who spent more than five years in a North Vietnamese prison after his Navy plane was shot down, was not a war hero.
The ill will grew after McCain voted in 2017 against a Republican replacement for the Obama-era health law. He doomed the bill with a dramatic thumbs-down on the Senate floor. Complaints about McCain's vote have become a staple of Trump's campaign speeches. He doesn't mention McCain by name but makes clear his intent by mockingly imitating the thumbs-down gesture.
The feud between the two men has persisted even amid the decline in McCain's health. While political leaders of both parties paid tribute to McCain and offered prayers Friday, Trump and the White House remained silent. Trump did not mention McCain or the health care vote in a speech Friday night at a fundraising dinner in Ohio.
Earlier this month, Trump signed a military policy bill named for McCain, but he made no mention of McCain at a signing ceremony.
The son and grandson of Navy admirals, McCain is a former Navy pilot. He was elected to Congress in 1982 and to the Senate four years later, replacing the retired Barry Goldwater.
Despite his famous stubborn streak and occasional orneriness, McCain is widely admired on both sides of the aisle, and tributes poured in Friday after the family announced the treatment decision.
"We are so fortunate to call him our friend and colleague," Senate Majority Leader Mitch McConnell said on Twitter. McCain, his wife Cindy "and the entire McCain family are in our prayers at this incredibly difficult hour," McConnell said.
Ducey called McCain "an American hero" who always put his country before himself.
A "spirt of service and civility" guided McCain's life, standing as a model for Americans regardless of political affiliation, Ducey said.
Cindy McCain tweeted that she loves her husband "with all of my heart" and thanked those who have cared for him.
McCain had surgery in July 2017 to remove a blood clot in his brain after being diagnosed with an aggressive tumor called a glioblastoma. It's the same type of tumor that killed Sen. Edward M. Kennedy, D-Mass., at age 77 in 2009.
McCain rebounded quickly, however, returning to Washington and entering the Senate in late July to a standing ovation from his colleagues. In a dramatic turn, he later cast the deciding vote against the Republican health care bill, earning Trump's enduring wrath.
McCain's condition worsened last fall, and he has been in Arizona since December. A source close to McCain who asked not to be identified said Friday the senator was at his Arizona ranch with his family.
He is a long-term survivor of melanoma, a deadly skin cancer. But doctors classified his brain cancer as a "primary tumor," meaning it's not related to his former malignancies.
McCain ran unsuccessfully for the Republican presidential nomination in 2000, then won it in 2008 before losing the general election to Obama.
When Republicans took control of the Senate in 2015, McCain embraced his new influence as chairman of the Armed Services Committee, pushing for aggressive U.S. military intervention overseas and eager to contribute to "defeating the forces of radical Islam that want to destroy America."
Asked how he wanted to be remembered, McCain said: "That I made a major contribution to the defense of the nation."
Former Connecticut Sen. Joseph Lieberman, a close friend, said Friday that "becoming John McCain's friend has been one of the great blessings of my life. Today I am praying for him and his family."
Mitt Romney, the GOP's 2012 presidential nominee, said on Twitter, "No man this century better exemplifies honor, patriotism, service, sacrifice and country first than Senator John McCain. His heroism inspires, his life shapes our character. I am blessed and humbled by our friendship."