The Conventional Wisdom states that a vice presidential pick really isn't that important. There's a lot of evidence to support that view: A bad CW pick, who either proves hapless or embarrassing -- like Sen. Dan Quayle, R-Ind., did for Vice President George H.W. Bush' title='George H.W. Bush' class='tpstyle'>George H.W. Bush in 1988 or Rep. Geraldine Ferraro, D-N.Y., did for Sen. Walter Mondale, D-Minn., in 1984 -- can weigh down a presidential candidate like a heavy anchor around the neck of a swimmer.

In fact, Bush coasted to an easy victory in 1988 against Massachusetts Gov. Michael Dukakis for the Democrats, even though Dukakis had one of the most impressive and effective vice presidential candidates in recent memory -- Sen. Lloyd Bentsen of Texas. And Mondale in 1984 was a dead duck up against President Ronald Reagan anyway. It wouldn't have mattered if he had chosen Bruce Springsteen as his running mate: He was going down, no matter what.

But there have been a number of occasions in American political history when choosing the right running mate did decisively tip the scales: Franklin Roosevelt would never have won the Democratic presidential nomination in the first place, back in 1932, had he not cut a deal with House Speaker John Nance Garner of Texas. Garner's support proved crucial in putting FDR over the top at the Democratic National Convention in Chicago.

Running at the height of the Great Depression, FDR probably would have beaten incumbent President Herbert Hoover handsomely anyway. But he had no standing or credibility in his own right among the vast agrarian, homeland wing of the Democratic Party in the South, Midwest and California.

"Cactus Jack" Garner, backed by former Treasury Secretary William Gibbs McAdoo and the then unmatched media power of William Randolph Hearst's INS wire service and national chain of newspapers, was able to rally that support for him in an irresistible tidal wave. Garner went on to serve two terms as one of the most powerful vice presidents in U.S. history.

In 1960 Sen. John Kennedy, D-Mass., had no trouble in winning the Democratic presidential nomination in his own right. He didn't need the support of Sen. Lyndon Baines Johnson of Texas for that. But he desperately needed Johnson's clout to carry Texas for him in one of the most nail-biting finishes in U.S. history. If JFK didn't put LBJ on the ticket, he would have lost. And from civil rights to the Apollo man on the moon program, Johnson proved to be a powerful vice president who pushed his favored causes with Congress and got things done.

Vice President Dick Cheney has been widely reviled by the left for his alleged exercise of exceptional power during President George W. Bush's two terms in office. Bush might not even have squeaked into the White House at all if it hadn't been for Cheney. The election ended up hinging on a tiny margin of a few hundred votes that decided the Electoral College clout of the state of Florida, with the fourth-largest population in the Union, would go to Bush. Several other states were decided in favor of Bush and Cheney by almost as narrow margins.

Cheney could boast an exceptional amount of experience, especially as the first President Bush's secretary of defense from 1989 to 1993. That resume reassured a lot of centrist voters that Bush would be an acceptable choice even though he had no national experience at the time.

Most of all, however, the choice of a running mate can help or hinder a presidential contender, especially one relatively new on the national scene, by suggesting to the public whether the fresh face has sound judgment.

Thus, the first President Bush could shrug off the embarrassment of Dan Quayle's gaffes in the 1988 campaign because his own record on the national scene was already so long and impressive.

The elder Bush had already served with distinction as ambassador to the United Nations, director of the Central Intelligence Agency and vice president. Similarly, when controversy erupted over the alleged financial improprieties of Sen. Richard Nixon of California in the 1952 campaign, it was water off a duck's back for the Republican nominee, five-star General of the Army Dwight D. Eisenhower, who had been supreme allied commander in the European Theater of Operations during World War II, U.S. Army chief of staff and the founding head of the North Atlantic Treaty Organization.

On the other side of the fence, the disastrous Geraldine Ferraro pick proved the coup de grace to Mondale's already doomed candidacy in 1984. Democratic Sen. George McGovern's embarrassing pick of Sen. Thomas Eagleton as his running mate in 1972 also didn't change history, but it too proved the final nail in the coffin for McGovern's political hopes against Republican White House incumbent Richard Nixon.

Obama, like his hero JFK in 1960, doesn't need to pick a powerful figure in the party to assure his nomination. But like FDR in 1932 or Texas Gov. George W. Bush in 2000, he needs an impressive choice that will reassure centrist voters worried about his lack of experience.

Who did he choose? We shall soon see.