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).