Republican presidential candidate John McCain stunned the US political establishment Friday and bolstered his image as a maverick by choosing the little-known female governor of Alaska as his running mate in the race again Democrat Barack Obama. Sarah Palin offers risks and rewards for McCain. The choice of a 44-year-old, first-term governor to be his vice president could undermine one of McCain's main campaign themes: that Obama, a 47-year-old first-term senator, is too inexperienced to become president. But Palin, whose nomination was announced Friday, could help McCain rally social conservatives, a core Republican constituency that has had an uneasy relationship with McCain. Palin has a strong anti-abortion record and opposes gay marriage. "I have found the right partner to help me stand up to those who value their privileges over their responsibilities, who put power over principle, and put their interests before your needs," McCain told a crowd of supporters. Choosing a young, female unknown from outside the continental United States could buttress McCain's reputation as an unconventional candidate. Palin has her own reputation as a maverick for taking on corruption in her state's Republican Party. Both McCain and Obama are running against the political status quo, but Obama keeps noting that McCain has been in Washington for decades. Palin could also help McCain's efforts to target supporters of former Democratic presidential candidate Hillary Rodham Clinton. Many Clinton backers are deeply disappointed that Obama upset her in the primaries, ending her campaign to become America's first female president, and then bypassed her for the vice presidency. "It turns out the women of America aren't finished yet and we can shatter that glass ceiling once and for all," Palin said at a raucous rally with McCain in the swing state of Ohio. However, working against Palin in that regard is that many Democratic women are strong supporters of abortion rights, which she strongly opposes. McCain's choice also means that no matter who wins in November, history will be made as either the first black man will become president or the first woman vice president. Vice presidential choices seldom have much effect on the presidential election. But McCain's choice received extra scrutiny because of his age and bouts with skin cancer. He turned 72 on Friday and would be the oldest, first-term president in US history. If he dies or is incapacitated in office, Palin would succeed him - a point stressed by Obama's campaign. "Today, John McCain put the former mayor of a town of 9,000 with zero foreign policy experience a heartbeat away from the presidency," Adrianne Marsh, a spokeswoman for Obama, said in a written statement. However, Obama and his running mate, Joe Biden, later issued a statement congratulating her and each followed that up with a personal phone call. Obama "told her she would be a terrific candidate," campaign spokesman Robert Gibbs said later. "He also wished her good luck, but not too much luck." McCain announced his choice of Palin three days before the start of the Republican National Convention in St. Paul, Minnesota. The announcement shifted attention from the Democratic convention in which Obama made history by becoming the first black presidential nominee of a major US party. McCain said he made his decision after looking for a political partner "who can best help me shake up Washington and make it start working again for the people who are counting on us." President George W. Bush complimented McCain for "an exciting decision." Palin has no international affairs experience and, in little more than a month, will be in a nationally televised debate with Biden, one of his party's leading voices on foreign policy and a quick witted, sharp-tongued public speaker. She is three years younger than Obama and a generation younger than Biden. But McCain said Palin was "exactly who I need. She's exactly who this country needs to help us fight the same old Washington politics of me first and country second," he said. Palin could help McCain muffle Obama's oft-repeated criticism that the Republican had little new to offer the country. She would also be the first female to take the No. 2 spot on the Republican ticket and only the second woman nominated for the job in US history. The first was Geraldine Ferraro who ran on Walter Mondale unsuccessful 1984 Democratic presidential ticket. "I am honored," she said as she stood by a beaming McCain in her first few seconds in the national spotlight. Palin reached out to Democratic women voters, praising the "determination and grace" of Clinton, who drew 18 million votes in her unsuccessful run against Obama for the Democratic nomination. Clinton said in a statement: "We should all be proud of Gov. Sarah Palin's historic nomination, and I congratulate her and Sen. McCain. While their policies would take America in the wrong direction, Gov. Palin will add an important new voice to the debate." McCain and Palin later started a bus tour across Ohio and to Pittsburgh, where they will hold a campaign rally Saturday. Ohio and Pennsylvania are two states that will be hotly contested this fall. Obama also joined Biden on a three-day bus tour of crucial industrial states that began with a visit to a biodiesel fuel plant in western Pennsylvania. McCain has been seen as the underdog in the presidential campaign, given the unpopularity of Bush, a fellow Republican. But he wiped out Obama's lead in opinion polls ahead of the Democratic convention, pressing the argument that Obama was unprepared to be president. Obama appeared to receive the boost in support that typically follows political convention. A Gallup poll released Friday showed him leading 49 percent to 41 percent. However, those figures could change after the Republican convention. By selecting Palin, McCain passed over several more prominent prospects who had figured in speculation for months - Minnesota Gov. Tim Pawlenty, former Massachusetts Gov. Mitt Romney and former Pennsylvania Gov. Tom Ridge among them.