The Arizona Republican, 81, announced that he was undergoing treatment for a primary glioblastoma last summer. He has remained in the state since December.
"In the year since, John has surpassed expectations for his survival. But the progress of disease and the inexorable advance of age render their verdict," McCain's family said in a statement Friday morning. "Our family is immensely grateful for the support and kindness of all his caregivers over the last year, and for the continuing outpouring of concern and affection from John’s many friends and associates, and the many thousands of people who are keeping him in their prayers. God bless and thank you all."
During his six terms in the U.S. Senate, McCain became one of the most respected lawmakers in Congress. He served in the Navy during the Vietnam War and spent five years in captivity. McCain ran for president in 2004 and 2008.
More recently, McCain made headlines as the subject of derision from then-candidate Donald Trump, who criticized the senator for being "captured" in Vietnam. He also gave us one of the more dramatic moments on the Senate floor in recent history, killing a repeal of the Affordable Care Act with a thumbs down during a late night vote.
McCain's announcement means that he almost certainly will not serve the rest of his term. In the event of the Senator's death, it would fall on Governor Doug Ducey to appoint a Republican replacement, who would serve until the 2020 general election.
Arizona leaders were quick to shower McCain with support praise.
In a statement, Ducey said, "John McCain is an American hero, always putting country before self. From Vietnam to the halls of the U.S. Senate, the spirit of Service and civility that has guided Senator McCain's life stands as a model for all Americans, regardless of political affiliation."
Senator Jeff Flake:
Congresswoman and Republican Senate candidate Martha McSally:
God bless and keep this wonderful man and his family @SenJohnMcCain— Jeff Flake (@JeffFlake) August 24, 2018
Congresswoman and Democratic Senate candidate Kyrsten Sinema:
John McCain's life has been one of service and sacrifice. His strength and resolve enabled him to endure 5.5 years as a prisoner of war, and to continue to serve his country for decades.— Martha McSally (@RepMcSally) August 24, 2018
Former Maricopa County Sheriff and Republican Senate candidate Joe Arpaio:
@SenJohnMcCain is not only an American hero who has sacrificed so much for his country, he’s Arizona’s hero. His strength and commitment to our great state and this country can’t be matched. I’m thinking of him and his family today and wishing them peace and comfort.— Kyrsten Sinema (@kyrstensinema) August 24, 2018
Dr. Kelli Ward, who opposed McCain in the 2016 Republican primary and his running again, said in a statement:
"This is a sad turn of events for Senator McCain and his family. As a doctor, I’ve seen these types of decisions made and it’s extremely difficult. While I’ve had differences with John McCain over the years, I wish him and his family comfort at this time.”