It's going to be ugly in Iraq no matter what. But leaving the soldiers hanging in a situation where they can neither leave nor advance but are consigned to mill around until an Iraqi insurgent gets lucky is the worst possible case. Either put enough forces in Iraq to win or get out.
Of course, the first will probably require a draft, and the second will be politically unpaltiable until the public is soundly against the war. It is likely to either canidate will fail this challenge, but a deadlock right now might insure it.
Jay