The main reason for the shrunken battlefield is the failure of both parties to land prized recruits. Time and again, top-tier potential candidates have decided the lure of the Senate isn’t strong enough to endure a grueling campaign that might or might not end well.

Former Democratic Gov. Brian Schweitzer, the party’s best hope of keeping Sen. Max Baucus’s seat in their column, was only the latest example when he opted July 13 not to run. Democrats haven’t turned up strong candidates in two states where members of their party are retiring, West Virginia or South Dakota, making them likely GOP pickups.

Republicans have had their own recruitment shortcomings. The party has yet to field quality candidates in purple and blue states that, if history and demographics are any guide, should be competitive.

The GOP also has yet to capitalize on Democratic retirements in Iowa and Michigan. The Democratic candidates, Reps. Bruce Braley of Iowa and Gary Peters of Michigan, have already cleared the field, while the GOP’s best options, Reps. Tom Latham and Mike Rogers, opted against running.