John S. McCain III, center, with his grandfather Vice Admiral John S. McCain Sr., at left, and father Admiral John S. McCain Jr. in a family photo from the 1940s.

McCain, front right, with his squadron in 1965. A Navy fighter pilot, McCain served in Vietnam and was awarded the Silver Star, Bronze Star, Legion of Merit, Purple Heart, Distinguished Flying Cross Medal, and Prisoner of War Medal.

On Oct. 26, 1967 Lt. Cmdr. McCain was rescued from Hanoi's Truc Bach Lake by several Hanoi residents after his Navy warplane was downed by the North Vietnamese.

A Vietnamese doctor examines McCain after he was captured in 1967. He suffered injuries in the crash when his plane was shot down and was subsequently tortured as a POW during his five years of imprisonment in Hanoi.

McCain is welcomed to Washington on May 24, 1973, by President Richard Nixon following his release after five-and-a-half years as a prisoner of war in Vietnam.

McCain and his wife Cindy, left, attend an election night event in Phoenix on Nov. 2, 1982. McCain launched his political career when he was elected to the U.S. House of Representatives from Arizona in 1982.

Sen. John Kerry, a fellow Vietnam veteran, and Sen. McCain examine a book on June 24, 1992 containing the names of the "total unaccounted for "soldiers who served in the Vietnam War. McCain was first elected to the Senate in 1983, after retiring from the Navy in 1981.

McCain holds photos of himself as a 30-year-old P.O.W. outside the Army Museum in Hanoi on Oct. 19, 1992. McCain served as a member of the Senate Select Committee on servicemen listed as missing in action (MIAs) in Southeast Asia. McCain is also known for his work towards restoring diplomatic relations with Vietnam.

Republican presidential candidate Bob Dole and McCain wave to members of the American Legion at the group's annual convention in Salt Lake City on Sept. 3, 1996. McCain was on Dole's short list of possible running mates. He had also been short-listed as a possible running mate for George H.W. Bush in 1988.

McCain visits the popular Shorja market in central Baghdad on April 1, 2007. McCain charged that the American people were not getting a "full picture" of progress in the security crackdown in the capital. McCain voted for the Iraq War Resolution in 2002, and began questioning troop levels as early as 2003.

Republican presidential hopefuls McCain, former Sen. Fred Thompson, Rep. Ron Paul, former Massachusetts Gov. Mitt Romney, former Arkansas Gov. Mike Huckabee and former New York City Mayor Rudy Giuliani participate in a televised debate on Jan. 5, 2008 in Manchester, New Hampshire.

McCain hugs his daughter Meghan after hearing that he was the projected winner of the New Hampshire Primary on Jan. 8, 2008.

McCain joins his running mate Alaska Gov. Sarah Palin and her daughter Piper at the end of her speech at the Republican National Convention in St. Paul, Minnesota on Sept. 3, 2008.

McCain and wife Cindy, joined by Gov. Sarah Palin and husband Todd, concedes the presidential race to Sen. Barack Obama on election night Nov. 4, 2008.

President-elect Barack Obama speaks with McCain at a bipartisan dinner honoring McCain in Washington on Jan. 19, 2009.

McCain, Sen. Charles Schumer, center, and Sen. Lindsey Graham talk on Feb. 12, 2013, before President Barack Obama's State of the Union.

McCain looks at the Roll of Honor at the Australian War Memorial in Canberra, Australia, on May 29, 2017.

McCain returns to the Senate with his wife Cindy on July 25, 2017. McCain had been recently diagnosed with brain cancer but returned on the day the Senate was holding a key procedural vote on President Donald Trump's effort to repeal and replace the Affordable Care Act. He voted yes on a motion to proceed to debate on Republican health care legislation but a few months later decided to vote against the Republican health care bill.

McCain speaks after receiving the 2017 Liberty Medal from former Vice President Joe Biden at the National Constitution Center on Oct. 16, 2017 in Philadelphia.

Army Chief of Staff Gen. Mark A. Milley and McCain watch a special Twilight Tattoo performance on Nov. 14, 2017 at Fort Myer in Arlington, Virginia. Sen. McCain was honored with the Outstanding Civilian Service Medal for over 63 years of dedicated service to the nation and the U.S. Navy.