Don't bet on a governor as Romney's running mate

Although the historical record is spotty on this, there is also some evidence that governors are at greater risk of getting themselves into very severe scandals than senators are. Historically, seven senators have either been expelled because of a scandal or have resigned under expulsion proceedings, not counting senators expelled for supporting the Confederate rebellion. By contrast, even though there are only half as many governors as senators, 11 have either been impeached, removed from office by court or resigned under impeachment proceedings, while another 11 governors have resigned under scandal before facing potential impeachment. And the only vice president to resign under scandal, Mr. Agnew, was a former governor.

The risk that a vice-presidential candidate might be viewed as unready by the voters is another thing that campaigns want to avoid — if the president dies and the phone rings at 3 a.m. in a national emergency, are they ready to take the call?

Here, although governors’ executive experience might otherwise be an asset, they will not usually have acquired foreign policy or national security experience, whereas senators can serve on foreign policy committees and must make votes and take positions on world affairs.