Vice President Joe Biden shakes hands with Sen. John McCain after administering the Senate oath of office during a mock swearing-in ceremony on Tuesday, Jan. 3, 2017. (AP Photo/Kevin Wolf)
U.S. Rep. John McCain III, R-Ariz., holds a photo of a marker in Hanoi at Truc Bach Lake where he parachuted after being shot down as a Navy pilot in the Vietnam War. (AP Photo/Jim Bourdier)
Sen. John McCain and Sen. Barack Obama shake hands at the conclusion of the presidential debate on Friday, Sept. 26, 2008. (AP Photo/Charles Dharapak)
Sen. John McCain, R-Ariz., leaves a closed-door session on Capitol Hill in Washington on Dec. 1, 2017. (AP Photo/J. Scott Applewhite)
Republican presidential candidate Sen. John McCain, R-Ariz., waves to supporters before speaking at a town hall-style meeting on May 29, 2008, in Greendale, Wisc. (AP Photo/Darren Hauck)
Sen. John McCain, R-Ariz., and Sen. Kent Conrad, D-N.D., arrive for an anti-tobacco rally on Capitol Hill, Wednesday, May 20, 1998. (AP Photo/Dennis Cook)
U.S. Sens. John McCain and Russell Feingold, co-recipients of the 1999 Profile in Courage Award, shake hands at the John F. Kennedy Library in Boston on Monday, May 24, 1999. (AP Photo/Elise Amendola)
Presidential hopeful Sen. John McCain, R-Ariz., speaks to senior citizens in Sun City, Ariz. on Wednesday, June 2, 1999. (AP Photo/Ken Levine)
Republican presidential hopeful Sen. John McCain signs papers at the Secretary of State's office in Concord, N.H., to get his name on the presidential primary ballot in 1999. (AP Photo/Jim Cole)
Sen. John McCain, R-Ariz., left, asks a question of Ashton Carter, President Barack Obama's choice to head the Defense Department, as he testifies on Capitol Hill on Feb. 4, 2015. (AP Photo/Susan Walsh)
Sen. John McCain and Sen. Hillary Clinton take part in the official dedication of the Center for the Intrepid at Fort Sam Houston in San Antonio, Monday, Jan. 29, 2007. (AP Photo/Eric Gay)
Sen. John Kerry gives Sen. John McCain his pilot's helmet on Capitol Hill in Washington, Dec. 2, 1992. (AP Photo/U.S. Senate)
President Bush is presented with the International Republican Institute's Freedom Award by Sen. John McCain at the IRI Freedom Dinner in Washington in 2005. (AP Photo/Charles Dharapak)
Sen. John McCain delivers the keynote address during the Columbia College commencement, Tuesday, May 16, 2006, in New York. (AP Photo/Mary Altaffer)
Sen. John Kerry, D-Mass., and Sen. John McCain, R-Ariz., a former POW in Vietnam, confer during a meeting of the committee on Capitol Hill in Washington, D.C., Aug. 4, 1992. (AP Photo/John Duricka)
Congressman John Murtha and Sen. John S. McCain walk with other members of the official election observer delegation sent to Panama on May 6, 1989. (AP Photo/John Hopper)
U.S. Navy Commander John S. McCain, a guest of the South Vietnamese government, visits the Holt orphanage in Saigon, Vietnam, on Oct. 30, 1974. (AP Photo/Dang Van Phuoc)
John S. McCain III is escorted by Lt. Cmdr. Jay Coupe Jr., public relations officer, on March 14, 1973, to Hanoi's Gia Lam Airport. (AP Photo/Horst Faas)
U. S. Sen. John McCain, R-Ariz., testifies in a Los Angeles courtroom Friday, Oct. 26, 1991, during the trial of former Lincoln Savings and Loan head Charles Keating. (AP Photo/Nick Ut)
Sen. John S. McCain III joined a group of GOP congressmen in asking Gov. Evan Mecham to resign his office, Jan. 16, 1988, at the state capital in Phoenix. (AP Photo/Rob Schumacher)
President Bush and Sen. John McCain, R-Az., right, share a word while on stage before addressing the troops at Fort Lewis, Wash., Friday, June 18, 2004. (AP Photo/Susan Walsh)
Republican presidential candidate Sen. John McCain and his wife Cindy, smile as confetti falls on them at the end of town hall meeting in Peterborough, N.H., on Jan 30, 2000. (AP Photo/Stephan Savoia)
Vice President Dick Cheney receives the 2001 Freedom Award by the International Republican Institute present to him by Sen. John McCain in Washington, Tuesday, Oct. 23, 2001. (AP Photo/Pablo Martinez Monsivais)
Sen. John McCain, R-Ariz., sits in his chief of staffs' office on March 22, 2001, in Washington. (AP Photo/Stephan Savoia)
Arizona Sen. John McCain testifies before the Senate Ethics Committee Friday, Jan. 4, 1991 at Capitol Hill. (AP Photo/John Duricka)
Senator John McCain speaks with a soldier from the Panamanian Defense Forces Sunday, May 7, 1989, in Panama City after he voted. (AP Photo/Matias Recart)
John McCain holds a photo of a monument that the Vietnamese have erected in Hanoi on Friday, Jan. 11, 1985. (AP Photo/John Duricka)
Over the past several decades, Sen. John McCain gained a reputation as a lawmaker who was willing to stick to his convictions rather than go along with party leaders. Take a look back at his life and career.