George McGovern, who ran for president in 1972 against Nixon, was an inspiration to anti-war liberals. McGovern, who was a bomber pilot during World War II, focused his later life on issues of hunger. NBC's Brian Williams reports.

Updated at 12:36 p.m. ET: George McGovern, the unabashedly liberal Democratic senator whose outsider campaign against President Richard Nixon led to a landslide defeat and the eventual reformation of the Democratic Party as a more centrist organization, died early Sunday, his family said in a statement. He was 90 years old.

McGovern died at a hospice in Sioux Falls, S.D., where he had been admitted Monday.

Kelly O'Donnell of NBC News contributed to this report. Follow M. Alex Johnson on Twitter and Facebook

Steve Hildebrand, a spokesman for the family, said in a statement to NBC News: "At approximately 5:15 am CT [6: 15 a.m. ET] this morning, our wonderful father, George McGovern, passed away peacefully at the Dougherty Hospice House in Sioux Falls, SD, surrounded by our family and life-long friends.

"We are blessed to know that our father lived a long, successful and productive life advocating for the hungry, being a progressive voice for millions and fighting for peace.

"He continued giving speeches, writing and advising all the way up to and past his 90th birthday, which he celebrated this summer."

Senior Democrats praised McGovern on Sunday as a visionary whose political sacrifices opened up the party to women and minority groups.

Although McGovern was ridiculed for many years for having led the Democrats to an overwhelming defeat against Nixon, former Sen. Gary Hart of Colorado, his 1972 campaign manager, argued Sunday that McGovern "helped save the Democratic Party."

In 1968, McGovern headed a committee that reformed the party's nominating process. In a column for Politico remembering McGovern on Sunday, Hart wrote:

Those rules were designed to open party participation, especially in nominating candidates, to women, minorities, and young people. The reforms succeeded and the Democratic Party opened itself up to democratic participation. The control of power-brokers and party bosses was broken. Decrepit political machines largely collapsed. ... We will never know the nature of a McGovern presidency. But someday the American Democratic Party will find a way to honor him as it should.

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President Barack Obama called McGovern "a statesman of great conscience and conviction," saying in a statement that "this hero of war became a champion for peace. And after his career in Congress, he became a leading voice in the fight against hunger."

Among the most prominent Democrats to get their political starts on McGovern's insurgent 1972 campaign were former President Bill Clinton and Secretary of State Hillary Rodham Clinton. In a statement Sunday, they lamented the passing of a "friend" and a "tireless advocate for human rights and dignity":

We first met George while campaigning for him in 1972. Our friendship endured for 40 years. As a war hero, distinguished professor, Congressman, Senator and Ambassador, George always worked to advance the common good and help others realize their potential. Of all his passions, he was most committed to feeding the hungry, at home and around the world. The programs he created helped feed millions of people, including food stamps in the 1960s and the international school feeding program in the 90's, both of which he co-sponsored with Senator Bob Dole. In 2000, Bill had the honor of awarding him the Medal of Freedom. From his earliest days in Mitchell to his final days in Sioux Falls, he never stopped standing up and speaking out for the causes he believed in. We must continue to draw inspiration from his example and build the world he fought for. Our thoughts and prayers go out to his family and friends.

Slideshow: George McGovern Ed Widdis / AP The life of former Democratic Sen. George McGovern, who lost the 1972 presidential election to Richard Nixon and gained fame throughout his career for his devotion to fighting hunger and opposing war. Launch slideshow

George Stanley McGovern was bomber pilot who flew 35 combat missions in World War II, earning the Distinguished Flying Cross. He became a history and political science professor after the war and was elected to Congress in 1958. He won the first of three Senate terms in 1962.

McGovern became an early critic of the Vietnam War and a leader of the Democrats' liberal wing, propelling him to a campaign for the Democratic presidential nomination in 1968 as an anti-war candidate.

Four years later, McGovern emerged at the top of the heap after a fractious campaign that divided the party between his corps of young, idealistic supporters and the more establishment organization of Sen. Edmund Muskie of Maine, who was the losing vice presidential candidate on the ticket with Hubert Humphrey in 1968.

McGovern lost to Nixon in one of the biggest landslides in history, winning only Massachusetts and the District of Columbia — Nixon even won McGovern's own state, South Dakota.

Many factors contributed to McGovern's defeat: the dirty tricks of the Nixon campaign, which soon exploded into the Watergate scandal that led to Nixon's resignation in 1974; unresolved differences with key Democratic leaders after the bitter campaign, including Humphrey and Sen. Edward Kennedy of Massachusetts; and the successful tarring of McGovern as a far-left fringe candidate by Republicans, which was summed up most succinctly in Vice President Spiro Agnew's dismissal of McGovern as the candidate of "amnesty, abortion and acid."

Particularly damaging was McGovern's failure to win the endorsement of organized labor, despite his strong pro-labor voting record. McGovern publicly feuded with AFL-CIO President George Meany, who strongly supported the war in Vietnam.

But the biggest blow probably was the Democrats' mishandling of the selection of Sen.. Thomas Eagleton of Missouri as their vice presidential nominee. In a 1986 interview on C-SPAN, McGovern said that party leaders were divided among several higher-profile possibilities, including Kennedy, and that he eventually settled on Eagleton because he was "everybody's second choice."

Within two weeks, it became public that Eagleton suffered from severe depression, having been hospitalized several times and, on at least one occasion, having undergone electroshock therapy. By Juy 31, 1972 — less than three weeks after he had been nominated, Eagleton witrhdrew and was replaced by Sargent Shriver, former director of the Peace Corps and a member of Nixon's administration as ambassador to France.

Nixon walked to victory, collecting 520 electoral votes to McGovern's 17.

He returned to the Senate, only to be defeated by Republican James Abdnor in the 1980 Reagan landslide. But over time, his reputation was rehabilitated, and he made a creditable showing — finishing fifth — in the 1984 Democratic presidential primaries, in which he ran as a peace candidate.

Through the years, McGovern insisted that his biggest mistake hadn't been taking such liberal stances — it was not having stuck to his liberal beliefs fiercely enough.

"If anything, I don't think the Democrats have been strong enough in clinging to their principle," he said in a 2011 interview with the Argus-Leader of Sioux Falls, S.D.

"You can say they were too ideological. Well, I don't think you hold political convictions just to be able to spout out a complicated philosophy or ideology. You try to support what you think is in the best interests of the country. My qualms with the Democrats in recent decades is they aren't strong enough in dissenting from policies that they should be able to see are against our best interest."

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