George McGovern, the U.S. senator who won the Democratic Party’s presidential nomination in 1972 as an opponent of the war in Vietnam and a champion of liberal causes, and who was then trounced by President Richard M. Nixon in the general election, died early Sunday in Sioux Falls, S.D. He was 90.

His death was announced in a statement by the family. He had been moved to hospice care in recent days after being treated for several health problems in the last year. He had a home in Mitchell, S.D., where he had spent his formative years.

In a statement, President Barack Obama called McGovern “a champion for peace” who was a “statesman of great conscience and conviction.”

To the liberal Democratic faithful, McGovern remained a standard-bearer well into his old age, writing and lecturing even as his name was routinely invoked by conservatives as synonymous with what they considered the failures of liberal politics.

He never retreated from those ideals, however, insisting on a strong, “progressive” federal government to protect the vulnerable and expand economic opportunity while asserting that history would prove him correct in his opposing not only what he called “the tragically mistaken American war in Vietnam” but also the U.S. invasions of Iraq and Afghanistan.

A slender, soft-spoken minister’s son newly elected to Congress — his father was a Republican — McGovern went to Washington as a 34- year-old former college history teacher and decorated bomber pilot in World War II. Elected to the Senate in 1962, McGovern left no special mark in his three terms, but he voted consistently in favor of civil rights and anti-poverty bills, was instrumental in developing and expanding food stamp and nutrition programs, and helped lead opposition to the Vietnam War in the Senate.

The war was the cause he took into the 1972 election, one of the most lopsided in U.S. history. McGovern carried only Massachusetts and the District of Columbia and won just 17 electoral votes to Nixon’s 520.

The campaign was the backdrop to the burglary at the Democratic Party headquarters in the Watergate Hotel in Washington, and by the Nixon organization’s shady fundraising practices and sabotage operations, later known as “dirty tricks,” which were not disclosed until after the election.

George Stanley McGovern was born on July 19, 1922, in a parsonage in Avon, S.D., a town of about 600 people where his father, Joseph, was the pastor of the Wesleyan Methodist Church.

The family moved to Mitchell, in southeastern South Dakota, when George was 6. He went to high school and college there, enrolling at Dakota Wesleyan University in Mitchell in 1940. After Pearl Harbor, McGovern joined the Army Air Corps, and before going overseas, in 1943, he married Eleanor Stegeberg, who had grown up with an identical twin on a South Dakota farm. They had met at Dakota Wesleyan.