How No. 1s Pick No. 2s

A high-priced lawyer, a low-priced lawyer and the tooth fairy are sitting at a table on which rests a $100 bill. The lights go out briefly, and when they come back on the bill is gone. Who took it? Obviously, the high-priced lawyer—the other two are figments of our imaginations.

Here is another such figment: People who vote for a presidential candidate because of that candidate's running mate. There may be such people, but have you ever met one?

Still, it is neither pointless nor premature to wonder who each of the four most likely nominees—Hillary Clinton, Barack Obama, Rudy Giuliani and Mitt Romney—might choose to run with. The question illuminates the different challenges the candidates face in cobbling together 270 electoral votes.

A presidential nominee can try to do one or more of four things with the vice presidential selection. The nominee can try to heal a divided party by selecting the strongest loser in the nomination contest (e.g., Ronald Reagan's selection of George H.W. Bush in 1980). The nominee can make a "Hippocratic oath" selection—one that does no harm. Such a running mate has done nothing embarrassing (when vetting potential running mates, the nominee's agents hope for candor when they ask, "What is it that your wife does not know?") and will not say something embarrassing in October.

The nominee can select someone who might attract a slice—ethnic, religious, ideological—of the national electorate. This assumes that lots of voters nationally will favor the top of the ticket because of the bottom of it. (See above: Imagination, figment of.) Most realistically, the nominee can select someone bland ("do no harm") from a state where the running mate might give the ticket a small boost but one sufficient to capture electoral votes otherwise unattainable. Such calculations are risky: John Kerry chose North Carolina's John Edwards, but lost that state, and the congressional district Edwards lives in, and even Edwards's precinct.

If Clinton wins the nomination with Obama a strong second, it will make no sense for her to select him. She will receive at least 90 percent of the black vote without him and she should not need help in Illinois, which has not voted Republican since 1988. She is a cautious calculator, comfortable around people she knows well. Her Senate office is across the hall from that of Evan Bayh, the preternaturally cautious former two-term governor of Indiana. Winning that state's 11 electoral votes—it has not voted Democratic since 1964—would seriously complicate any Republican's path to 270. If she wants to reach for a bigger electoral-vote prize without removing a Democrat from the Senate, there is Ted Strickland, the popular governor of the Center of the Universe Every Fourth Year, a.k.a. Ohio (20 electoral votes).

As the Democrats' nominee, Obama's largest vulnerability would be his inexperience regarding foreign and military affairs. He could pick a former four-star Army general with diplomatic experience brokering peace in the Balkans—Wesley Clark. Or if Obama worried that such a choice might indicate insecurity, he could pick the governor of a Red—actually, an increasingly purple—state and turn it Blue: Tim Kaine of Virginia (13 electoral votes), which has not voted Democratic since 1964.

If Romney is the Republican nominee, that will indicate that he has assuaged social conservatives' suspicions about his late conversions to their causes. If Giuliani is the nominee, that will be in spite of the fact that social conservatives remain wary. Many of them might stay home in November 2008 to ensure a "purposeful loss" that teaches the party not to choose pro-choice nominees.

Giuliani's biggest weakness is his personal history and his weakest region is the South, where almost 40 percent of Republicans live. He could select the guitar-playing former governor of Arkansas Mike Huckabee, the Baptist minister who is as cuddly as Giuliani is abrasive. Giuliani would have to hope that Huckabee would stifle his impulse to say entertaining but idiotic things, such as: We can be energy independent in 10 years and then tell Saudi Arabia we "have about as much interest in their oil as we do their sand."

Romney might be the most unconstrained of the four in selecting a running mate. A former business executive, he is partial to people who have run large entities, which would point him toward other governors. That would reinforce his theme that Washington cannot be improved by people acculturated to its milieu. Because the winner of the presidency usually wins a majority of the states in the Mississippi Valley, Romney might select Matt Blunt, 37, of Missouri, the bellwether state: It is the only state that has voted with every presidential winner since 1956. Or Minnesota Gov. Tim Pawlenty, who turns 47 this week. Minnesota (10 electoral votes) is the only state that has voted Democratic in eight consecutive presidential elections.

Few voters will vote for the running mate rather than the person who chose him. But many voters might vote for the person at the top of the ticket because of what the bottom of the ticket says about the person at the top. Actually, most of those at the top of tickets probably regret the 12th Amendment. Before it was ratified in 1804, presidential nominees did not have the nuisance of running mates.