Trump has done little to hide his disdain for McCain, a former Republican presidential nominee and decorated Vietnam veteran. Using his political weight, the 81-year-old tried to undermine Trump's candidacy from within the party, eventually leading to a full-blown rift between both men. "But John came to NY and campaigned for me on the streets of Brooklyn".
As a naval aviator, McCain flew several missions off of the USS Intrepid aircraft carrier beginning in 1960.
Obama, who triumphed over McCain in the 2008 election, said that despite their differences, McCain and he shared a "fidelity to something higher - the ideals for which generations of Americans and immigrants alike have fought, marched, and sacrificed".
"My deepest sympathies and respect go out to the family of Senator John McCain".
The McCain-Trump relationship grew heated in 2015 when McCain said Trump's candidacy had "fired up the crazies".
"John McCain's life is proof that some truths are timeless".
Both Vietnamese people and US citizens in Hanoi have flocked to the grey, concrete monument to offer flowers, incense, flags and other tributes to McCain.
Arizona operatives speculate that one of two former congressmen from the state, John Shadegg and Matt Salmon, could fill the seat.
"But I think with that we had a chance to understand each other more after the war, and you were the one that made a major contribution to building up that link". He loved me, and I loved him.
The Vietnam War killed an estimated 2.5 million northern Vietnamese fighters, 58,000 American servicemen and some three million civilians before its end in 1975, two years after McCain was released and sent home.
Tributes to McCain, meanwhile, poured in from other world leaders and statesmen including former presidents Barack Obama and George W. Bush.
Hollywood Life said that Melania has pushed Donald Trump to express himself in a honest way about McCain's passing and to do something honorable for the family of a man who contributed so much to this country. Others have included 11 USA presidents dating to Abraham Lincoln, including four who were assassinated; two vice presidents; six other members of Congress; three military leaders; and the unknown soldiers from World Wars I and II, the Korean War and the Vietnam War.
Trump and McCain had feuded for years, most notably in 2016 when Trump said McCain was "not a war hero" because he had been captured in Vietnam. Jeff Flake, lamented on CNN how hard it would be to go on without McCain.
Tributes to McCain continued to pour in from former U.S. presidents, members of Congress and foreign leaders while Trump golfed on Sunday. He spent years as a prisoner of war at Hoa Lo prison - or the "Hanoi Hilton", as it was known to American soldiers.