Former Sen. George McGovern, the 1972 Democratic presidential candidate and an early backer of Hillary Rodham Clinton, joined a noisy rally for Barack Obama on Friday night, describing the Illinois senator as a "ripple of hope" who can win the White House.

McGovern has shifted his allegiance to Obama and suggested it's time for Clinton to pull the plug. He offered an explanation to a cheering crowd of 6,500.

"Last October, I endorsed Senator Hillary Clinton," said McGovern. "She and her remarkable husband, President Clinton, way back 36 years ago worked their hearts out for me in that 1972 presidential campaign. While I endorsed Senator Obama, the Clintons have remained my treasured friends."

He described Obama's lead as "insurmountable" and argued "Democrats need to be gathering in a united way behind him."

Obama's campaign said support from the 85-year-old former South Dakota senator and others such as former Sen. Tom Daschle, D-S.D., is important because they remain popular figures among the state's Democrats.

"They've been around forever," said aide Steve Hildebrand, formerly a South Dakota-based consultant. "They all have 90 percent-plus approval ratings."

Republicans took notice of McGovern's support for Obama, gleefully issuing a reminder of how McGovern's campaign turned.

"Why is Obama continuing to campaign with landslide loser George McGovern?" the Republican National Committee asked in a statement. Richard Nixon carried 49 states and won the election with 520 electoral votes. McGovern got 17.