The criticism, consternation and cacophony surrounding John McCain's selection of Sarah Palin as his vice-presidential candidate highlights a fundamental truism of American politics, namely, that while a veep pick only marginally aids the presidential nominee in winning the support of independent voters, it can significantly enhance his credibility and solidify the party base.

Over the past half-century, dating back to 1952, presidential candidates with substantial stature have chosen nonentities for veep: Dwight Eisenhower picked Richard Nixon in 1952, Nixon picked Spiro Agnew in 1968, George Bush picked Dan Quayle in 1988, and McCain picked Palin in 2008. At the time of their nominations, Eisenhower, Nixon, Bush and McCain were deemed to have the stature to be president, and their vice-presidential pick was deemed inconsequential.

Conversely, candidates lacking stature have chosen those with greater credentials as their running mate: George W. Bush picked Dick Cheney in 2000, and Barack Obama picked Joe Biden in 2008.

A vice-presidential selection fulfills one or more of five key criteria and is designed to placate, compensate, aggregate, ameliorate, actualize or energize key constituencies of the party. Here's an analysis:

Placation: In 1980 Ronald Reagan placated Republican moderates by choosing George Bush, the runner-up for the nomination, as vice president. With a united party, Reagan obliterated President Jimmy Carter. In 1976 Gerald Ford tried to placate disgruntled conservatives by asking Reagan to be his running mate. Reagan wisely declined. Ford then picked Bob Dole, hoping the acerbic Kansas conservative would placate Reaganites. Dole didn't, and Ford narrowly lost.

In 1952 Illinois Governor Adlai Stevenson had a liberal reputation and a reformer image. In a party then dominated by southerners, he was anathema. After winning the nomination, he picked John Sparkman of Alabama -- an economic liberal and a racial segregationist -- for vice president. Stevenson won most of the habitually Democratic Deep South but lost Texas, Virginia, Florida and Tennessee to Eisenhower.

In 1976 Carter, the Georgia governor running as an "outsider," placated the Washington Democratic establishment by picking Minnesota Senator Walter Mondale. Likewise, in 1988 Mike Dukakis, the Massachusetts governor running as a "reformer," placated nervous Washington Democrats by picking veteran Texas Senator Lloyd Bentsen.

In 1964 President Lyndon Johnson, who succeeded the assassinated John Kennedy, was under enormous pressure to name Bobby Kennedy as his vice president, so as to both grasp the Kennedy mantle and to placate Democratic liberals. But since the Republicans had nominated a sure loser, Barry Goldwater, Johnson decided that he didn't need a Kennedy on his ticket or want Bobby to remain as the attorney general in his administration. Had a Johnson-Kennedy ticket triumphed, pundits and politicians would have credited Kennedy for the win.

Johnson instead chose Hubert Humphrey, a liberal Minnesota senator, which satisfied the Democratic left, and he went on to trounce Goldwater.

Compensation: Any presidential nominee wants to overcome any ideological or chronological shortcomings.

An older candidate wants a younger running mate - such as Eisenhower-Nixon (1952 and 1956), Reagan-Bush (1980 and 1984), Dole-Kemp (1996) and McCain-Palin (2008). A younger candidate wants an older running mate - such as Kennedy-Johnson (1960), Dukakis-Bentsen (1988), Bush-Cheney (2000 and 2004) and Obama-Biden (2008). That helps neutralize the experience issue.

For the Democrats, a liberal presidential candidate seeks a somewhat conservative running mate, as Dukakis did in 1988 and Obama did in 2008; conversely a more moderate candidate, such as Carter in 1976, seeks a liberal partner.  Ideological balance is important.

Aggregation: Up until 1960 a key criterion for picking a vice-presidential nominee was his ability to carry his state, in order to win a close election. That's why William McKinley picked Teddy Roosevelt of New York in 1900, why Tom Dewey picked Earl Warren of California in 1948, and why Kennedy picked Johnson of Texas in 1960. Geography is now irrelevant, having been superseded by constituencies based on gender or race.

At one time, when party bosses dictated the outcome of national conventions, the veep selection was occasionally traded for votes. That occurred regularly in the 1800s, and it was how Franklin Roosevelt won in 1932, when he made John Garner the vice-presidential nominee in exchange for support of the Texas delegation.

Interestingly, that situation could have arisen at the 2008 Democratic convention, had Obama and Hillary Clinton been deadlocked, with neither having a majority. Then one could have offered an opponent's supporter the number two spot in exchange for votes, or they would have had to agree to an Obama-Clinton or Clinton-Obama ticket. But, had Obama's campaign collapsed, he would not have been offered the vice-presidential spot.

Actualization: Occasionally a nominee picks a vice president because he wants him to be his successor. That wasn't the case with Eisenhower and Nixon, Kennedy and Johnson, or Bush and Cheney. It definitely was the case with Johnson and Humphrey (1964), and it probably was a consideration in Humphrey's choice of Ed Muskie (1968), Carter's choice of Mondale (1976), Reagan's choice of Bush (1980) and Bill Clinton's choice of Al Gore (1992).

Amelioration: In some cases, the vice-presidential selection is a political minefield, with the ultimate choice antagonizing many and pleasing few. That was Nixon's quandary in 1968: choosing Nelson Rockefeller or Chuck Percy would infuriate the conservatives, and choosing Reagan would appall the liberals. So he picked the nondescript Agnew, who enraged nobody.

Nixon, as vice president in 1960, had a similar dilemma. Conservatives wanted Goldwater and liberals wanted Rockefeller for the second spot. So Nixon opted for a party elder statesman, United Nations Ambassador Henry Cabot Lodge -- a horrendous choice. While Johnson delivered Texas -- and the election -- to Kennedy, Lodge was worthless to Nixon.

The elder Bush faced a similar situation in 1988. Hard-core Reaganites did not view him as the president's true successor: Dole, Kemp, Pete DuPont and Alexander Haig sought the nomination, and Reagan's reported choice was Paul Laxalt of Nevada. But Bush won the primaries, and he instinctively understood that his presidency could not be Reagan's so-called "third term." He had to pick a running mate acceptable to the Reaganites, but not a Reaganite. So he chose the obscure Quayle, a conservative Indiana senator who was disliked by nobody.

Energizing: A nominee with fervent appeal to their respective party's ideological bases cannot win the presidency -- witness Goldwater in 1964 and Democrat George McGovern in 1972 -- but a more moderate or mundane nominee needs a running made with some notoriety and unique appeal to his party's base. That's why the bland Mondale chose a woman, Geraldine Ferraro, in 1984. Ferraro was chosen to electrify women and liberals, but Mondale was still crushed by Reagan.

That's why the elderly Dole picked Jack Kemp in 1996, but Kemp failed to electrify Republican conservatives, and Dole lost to Clinton.

And that's why McCain picked Palin. She is young (44), ardently conservative, a hunter and 2nd Amendment protector, pro-life and a political "outsider." She makes McCain look like a moderate, and she energizes the social conservative base in the Republican Party.

Had McCain picked a white male, such as Mitt Romney, Mike Huckabee, Chuck Hagel or Joe Lieberman, the public and press reaction would have been tepid. But Palin does for McCain what Ferraro did for Mondale, namely, give the ticket some verve and color.

The current knock on Palin is that she is inexperienced. She doesn't have the resume of Biden, Cheney, Gore, Kemp, Lieberman, Mondale, Dole, Muskie, Humphrey, Johnson, Lodge or Nixon.

She has been governor of Alaska since January of 2007, and she was the mayor of Wasilla, a suburb of Anchorage, for 6 years, and a city council member for 4 years. That gives her just shy of 8 years of administrative experience and 4 years of legislative experience. That's more than Agnew, who was the governor of Maryland for 2 years and a county executive for 4 years. That's more than John Edwards (2004), who was a senator for 6 years. That's more than Sargent Shriver (1972), who was the Peace Corps director and the ambassador to France.

The bottom line:  Both 2008 vice-presidential choices were astute and calculating. The election outcome will demonstrate which was the shrewdest.