Ex-Sen. George McGovern, 90, is "no longer responsive" in hospice care, according to his family in a statement issued late Wednesday.
He was admitted to Avera McKennan Hospital in in Sioux Falls two days ago "with a combination of medical conditions, due to age, that have worsened over recent months," CNN cited the statement as saying.
His daughter, Ann McGovern, told The Associated Press that her father, a decorated World War II airman, was "nearing the end" and appeared restful and peaceful.
McGovern, the Democratic presidential candidate whose platform included ending the war in Vietnam at a time when the country was torn over American involvement there, lost to Richard Nixon in 1972.
According to the Hollywood reporter, his was the first Democratic campaign to rely extensively on Hollywood contributions.
Max Palevsky, Norman Lear, Stanley Sheinbaum and Harold Willens were among those who donated a total of more than $4 million to McGovern's campaign, while such celebrities as Warren Beatty and sister Shirley MacLaine appeared for him on the campaign trail.
He represented South Dakota in the US House from 1957 to 1961 and a US senator from 1963 to 1981.
In later years, he focused on combating world hunger.
McGovern's family asked Wednesday that people to donate to Feeding South Dakota in honor of the senator.