It must have seemed like a good idea at the time. In February 2009 a new Democratic president reached across party lines and nominated a Republican senator, New Hampshire's Judd Gregg, as commerce secretary. Putting a Republican in the cabinet would give Barack Obama's administration a bipartisan gloss while also benefitting the president's own party in the Senate by allowing the Granite State's Democratic governor to appoint a Senate replacement, leaving the Democrats just one seat short of a filibuster-proof 60-seat supermajority.

It...