WASHINGTON - Will John McCain's pick of a "dark-horse" - Sarah Plain - as his running mate on the Republican ticket pay off? That is the question being asked by political observers and analysts after McCain' s surprise choice rocked the political scene here. While Democratic presidential candidate Barack Obama played it very safe in naming his vice-president - Senator Joseph Biden, a foreign policy expert - his Republican opponent took a huge risk. Beating all media and public expectations, McCain made a bold decision to pick the 44-year-old and not-so-well-known female governor of Alaska Ms. Palin as his running mate. Opinion polls show that McCain and his Democratic opponent Obama virtually run even among male voters.  But among women voters, McCain is lagging behind by about 13 points at the present. That follows a traditional pattern: In recent decades, Democratic presidential candidates always enjoy a comfortable lead against Republicans among female voters. However, it is a little bit different story this year after Hillary Clinton, once aspiring to be the first female president of the United States, was defeated by Obama in a fierce contest for the Democratic presidential nomination. However, Obama's triumph left behind tensions between his supporters and Mrs Clinton's fans, including many middle-aged and elder women. The latest results of a Gallup poll shows that even after Mrs Clinton and her husband, former president Bill Clinton, threw their full support behind Obama, about 21 per cent of her supporters still said they haven't made up their minds to support Obama or they will vote for McCain instead. The McCain camp thus hopes they can use the sentiment to make inroads into the Democratic base, especially women. When she accepted McCain's offer at a rally in Dayton, Ohio, Palin made an explicit appeal to Mrs Clinton's voters. "Hillary left 18 million cracks in the highest, hardest glass ceiling in America," she said, "but it turns out the women of America aren't finished yet and we can shatter that glass ceiling once and for all." Analysts said although the majority of female Democrats may not change their choice because of Ms Palin, but in a close race, a certain number of defectors will make the difference. McCain chose Ms Palin also because as a conservative, she can help him mend fences with the conservative wing of the Republican Party. "I predict any conservatives who have been lukewarm thus far in their support of the McCain candidacy will work their hearts out between now and November for the McCain-Palin ticket," says David Keene, president of the American Conservative Union. Another reason for McCain to pick Ms Palin, brought up in a middle-class family in Alaska, is that she can help him to connect with white blue-collar voters better, especially in the so-called swing states like Ohio, Pennsylvania and Michigan. The biggest strength of Obama, analysts say, is that he is seen as an "agent of change" in a time when 80pc of the Americans say their country is on a wrong track. In the just-concluded Democratic National Convention, Obama again made a pledge to change the country's direction, restoring confidence at home and US reputation abroad. As the candidate for the ruling party, McCain faces challenges to be seen as an "heir" to the unpopular sitting president, George W Bush. NBC political analyst Chuck Todd said the choice of Ms. Palin made it clear that McCain has realized he can't beat the trend of "change" and must embrace it by choosing someone has a reputation of reformer like Ms Palin. As the governor of Alaska, Ms Palin has confronted her own party establishment to fight corruption and waste. She has earned the reputation of a "reformer" and a "clean" politician and enjoys an 80-per cent support rate in her state. John Pitney, a political scientist at Claremont McKenna College, said, "The public stereotype of a Republican is a wrinkled old guy taking cash under the table. One way for Republicans to break the stereotype is with a female reformer." Conservative commentator Pat Buchanan called it "the biggest political gamble, I think, just about in American political history."   But Ms Palin's lack of national politics experience effectively undercuts one of McCain's major argument against Obama: inexperience.  There's only 10 weeks to go before the general election in November, and to train Ms Palin into a good fighter at the national stage is not a small task. The gap of experience in foreign policy and national security affairs between Ms Palin and her Democratic opponent Sen Biden, who has served in the Senate for over three decades and is currently the chairman of the Senate Foreign Relations Committee, will be a big challenge. The two will have a national televised debate on Oct 2 and Ms Palin will have to make her own case for the issues that she is not so familiar with. Analysts said McCain knows the risk of making such a choice for running mate, but in a very bad year for the Republicans, he seems to be convinced that if he does not take some risks, he may certainly lose the whole race.