Give yourself a break. Save yourself some precious time. Stop reading any stories, leaks or rumors about who will be John McCain's or Barack Obama's vice-presidential picks. In the first place, nobody — almost certainly including McCain and Obama — knows, and in the second place, it's a good bet that whoever ends up being chosen will have next to no impact upon who wins on Nov. 4.

Think about it. In 1988, Democrat presidential nominee Michael Dukakis selected as his running-mate Texas Sen. Lloyd Bentsen, while Republican nominee George Herbert Walker Bush named Indiana Sen. Dan Quayle. In that year's vice-presidential debate, Bentsen so dominated, even humiliated, Quayle that if the debate had been a professional boxing match, the referee and the ringside physician would have stopped the one-sided fight.

What was the result? Bush-Quayle carried 40 of the 50 states, including Bentsen's (and Bush's) home state of Texas.

In fact, in the last half-century, the one vice-presidential candidate who did make a difference was Lyndon Johnson in 1960, when he, running with Northern Catholic presidential nominee John Kennedy, was able to convince enough white Southern Democrats that Kennedy was acceptable and would not be taking orders over a hotline from the Vatican.

Here is what you do need to know about vice-presidential choices. Does the nominee make a "micro" choice or a "macro" choice? A micro choice would mean picking a running mate who would help carry one important state. For example, in 2000 Democrat Al Gore, instead of choosing Connecticut's Sen. Joe Lieberman, could have selected the enormously popular senator and former governor of Florida, Bob Graham. With Graham, Gore carries Florida and goes to the White House, and George W. Bush returns to the governor's chair in Austin.

Bush in 2000 made a "macro" choice when he named Dick Cheney, former secretary of defense, White House chief of staff and respected House member, as his running mate. Bush would have carried Cheney's home state with Rosie O'Donnell on his ticket, but Cheney filled out Bush's painfully thin resume in foreign policy and national defense.

Micro choices for John McCain would include Florida's Gov. Charlie Christ, former Pennsylvania Gov. Tom Ridge or former Ohio congressman and Bush budget director Rob Portman.

Macro McCain possibilities would be (ethnic-religious-youth) Louisiana's 36-year-old Indian-American Catholic convert reform Gov. Bobby Jindal, (gender) Texas Sen. Kay Bailey Hutchison or (outside the box) Connecticut Independent Democrat Joe Lieberman — which at the very least would qualify two-time VP pick Joe for the Guinness Book of Records.

For Obama, micro choices would begin with popular Ohio Gov. Ted Strickland, the architect of Hillary Clinton's victory in his state's primary and a former Methodist minister, Florida senator and former astronaut Bill Nelson or former Virginia governor and current U.S. Senate nominee Mark Warner.

If Obama's perceived weakness in national security issues is a major concern, then a logical macro choice might be Virginia senator and much-decorated combat Marine veteran of Vietnam, Jim Webb, who has written lyrically about the history of his Scotch-Irish ancestors — many of whom live along the Appalachian Trail and most of whom have been quite cool toward Obama's candidacy.

Other macro possibilities: Former Senate defense leader Sam Nunn of Georgia, former Marine general and Centcom commander Anthony Zinni — like Webb, an early and outspoken opponent of the U.S. invasion and occupation of Iraq.

So, there you have it. Chances are good that none of the people on this page will be chosen. Remember that in spite of all the disclaimers from ambitious politicians that they do not want to be chosen, as a wise man once observed, the vice-presidential nomination is like the last cookie on the plate — everybody says he doesn't want it, but somebody always takes it.

To find out more about Mark Shields and read his past columns, visit the Creators Syndicate web page at www.creators.com.

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COPYRIGHT 2008 MARK SHIELDS