Prominent anti-Vietnam war campaigner Eugene J McCarthy has died at his Georgetown retirement home, aged 89.
McCarthy's 1968 campaign persuaded Johnson to step down
The former Democratic Minnesota senator ran for president five times.
He helped oust sitting President Lyndon Johnson in 1968, when his anti-Vietnam campaign was so strong it persuaded him against running for re-election.
"He was thoughtful and he was principled and he was compassionate and he had a good sense of humour," his son Michael told the Associated Press.
He said his father passed away in his sleep at the retirement home where he had lived for the past few years.
He said a private burial was planned for next week and that there would also be a memorial service in Washington.
Born in 1916, McCarthy was a member of the House of Representatives from 1949 to 1959 and the Senate from 1959 to 1971.
He was a civil rights campaigner and wrote poetry.
His biggest impression on US politics came in 1968, when he challenged the sitting president for the Democratic presidential nomination.
Lyndon Johnson was overseeing the US war in Vietnam, which McCarthy opposed.
Recruiting idealistic young volunteers known as "clean-for-Gene kids", his campaign grew in strength until the New Hampshire primary, when McCarthy got 42% of the vote.
The result so embarrassed Johnson, that the president withdrew from the race.
Competition for the 1968 nomination included Robert Kennedy - who was assassinated during the campaign - George McGovern and Hubert Humphrey.
Humphrey eventually prevailed, but was beaten in the election by Richard Nixon.
"It was a tragic year for the Democratic Party and for responsible politics, in a way," McCarthy later said.
"The party became a kind of unrelated bloc of factions... each refusing accommodation with another, each wanting control at the expense of all the others."
Critic of Bush
McCarthy left the Senate in 1971, but returned to seek the Democratic nomination in 1972.
He then left the Democrats and ran as an independent for the presidency in 1976.
McCarthy was annoyed his poetry was overshadowed by his politics
In 1988, he ran on behalf of a collection of left-wing state parties, and in 1992 returned to the Democrats to seek their nomination.
"He's obviously going to be remembered for the campaign in 1968, but I think he would also want to be remembered for the work he did in the early years of the civil rights movement," his son Michael told CNN on Saturday.
"I think he would enjoy being remembered as a contrarian."
After the 11 September 2001 attacks on the United States, he said the US was partly to blame for ignoring the plight of Palestinians.
"You let a thing like that fester for 45 years, you have to expect something like this to happen... No-one at the White House has shown any concern for the Palestinians."
He was a stern critic of President George W Bush, whom he labelled an "amateur".
His son Michael said the politician was also survived by daughters Ellen and Margaret, and six grandchildren.