The Dems will split on the War.
Those whose synapses actually fire will see that withdrawal is strategically unacceptable. Those for whom rationality long ago left the building will require immediate withdrawal.
Look for a political bloodbath in that party. This is McGovern v. Scoop Jackson all over again.
I predict anti-war protesters to take it to the Dems for the next two years, to the detriment of their party. Michael Moore and his ilk will become disillusioned (with the rational Dems), and leave the party for a splinter A.N.S.W.E.R.-inspired third party.
Could be worse.
Only if Bush holds firm. If the Democrats are forced to vote to withhold funds they will split and lose, but I'm not sure Bush won't back down first.