We have not even reached the upcoming Democratic South Carolina primary yet, and already the Presidential withdrawals are mounting.

On the Republican side, former Senator Fred Thompson today joined Congressmen Tom Tancredo and Duncan Hunter on the Republican side in the withdrawal column. Democratic Senators Joe Biden, head of the Foreign Relations Committee, and Chris Dodd, head of the Banking Committee, have already withdrawn.

Withdrawals have a cumulative effect, both forcing onetime middle tier candidates into the bottom tier and making withdrawals more socially acceptable and politically predictable.