By Madison Powers, CQ Guest Columnist

Speculation on vice presidential prospects is risky business. Not that there is much at stake in being wrong. No one is going to remember, unless by some miracle you guess right. In fact, the chances are very good that any guess will be wrong. Nonetheless, the temptation exists, especially when the only interesting American political news story in the dog days of summer is happening on foreign soil.

But it is the very fact that Barack Obama ’s world tour is so carefully choreographed that it invites speculation about who else has been selected to be on stage with him this week and how their auditions as surrogates or team mates are going. An even stranger thing to watch for is whether there turns out to be anything to Robert Novack’s blog post suggesting that Sen. John McCain might name a VP selection this very week just to nudge his way back into the news.

Sens. Jack Reed and Chuck Hagel are traveling with Obama. Or more accurately, Obama is in Iraq and Afghanistan as part of the more senior Reed’s delegation. Both have been mentioned as VP possibilities. Both look good as foreign policy and national security stage props. Both are thoughtful, educated men with distinguished military service records and unquestionable commitments to the well-being of those in uniform and those they serve.

Meanwhile, back home it is Sen. Evan Bayh who seems to be doing most of the long-distance color commentary for the domestic audience on how well the Obama trip is going. Not that it is needed, since all three network anchors have been dispatched for their summer vacations with Obama.

At least some rules or basic principles for VP have become part of the conventional wisdom, and they are worth remembering before the inherent merits of any particular prospect carry us away into the realm of fantasy.

First of all, neither candidate can choose a running mate who is on the wrong side of his party’s official position on abortion. If a candidate strays on this issue in the selection of a vice-president, it shows that he might go wobbly when nominating a Supreme Court justice. That throws out Hagel on the Democratic side and all sorts of moderates on the Republican side, including Tom Ridge.

Second, given the delicate balance of power in the U.S. Senate it would be a serious error to pick a senator from a state where a replacement from the state is not likely to be from the same party. That means making sure you know who the governor is before go poaching senators who governors name to fill out the remainder of the term. And it means not grabbing up the only viable red state candidate in a blue state or vice versa. That principle makes Virginia Sen. Jim Webb a bad choice, even though by most lights he would fit the bill in every other way.

Just in case the election does turn out to be about the economy, Webb would offer a double bonus. Not only has he military and national security credentials, his brand of economic populism could be a plus.

The third principle is not to choose someone who outshines or embarrasses the candidate. In Obama’s case there is not much risk of being eclipsed. In McCain’s case, well, you know the story. But either candidate could pick someone who might say something off-script or speak infelicitously. In an election year rife with verbal gaffes, cell phone recordings, and a bolus of public apologies, this may well be one thing that really matters.

Of course, you have to vet the spouse for this one as well. He or she has to enroll in some sort of crash course “Stepford” program designed to make sure that absolutely nothing of interest or with a spark of humor or humanity comes out of his or her mouth. Besides, having to reject and repudiate people with long close personal histories is hard to do in a convincing manner. Congressman Jesse Jackson Jr., however, has now given us reason to rethink the possibilities.

The fourth principle is that a VP candidate should add something to the ticket. This used to be virtually the sole consideration. This one is now optional. Principles 1-3 are mandatory. The first three principles point to things a presidential candidate must not do. They mirror the old adage “first do no harm.”

Burnishing the credentials of a candidate who lacks or is seen to lack bona fides in some area is a bonus. The choice of a VP based on what the VP adds to the ticket – think of Johnson for Kennedy – is no longer the main concern. The priority now is to think first of what evils must be avoided.

Once all the people who can’t pass muster on the “do no evil” test are eliminated the options dwindle. Hillary Rodham Clinton fails on several counts. She has the potential to outshine the candidate among some audiences, and the risk of embarrassment by her husband is considerable.