Why not, the War Powers Act seems pretty clear that he needs prior approval unless America is under attack or under a serious threat. Neither exception applies in this case.
It's an impeachable offense, if he does it without their approval. However, I think a resolution reprimanding him would be more likely to be successful and avoid letting him set a new precedent.
The Constitutionality of those provisions is very much in doubt. When Bush went to Congress prior to Iraq, his message in response to the resolution made it clear that the White House was not agreeing that there was a Constitutional obligation to obtain Congressional approval.
Impeachment would never get out of the House in this circumstance. The Republicans are split on the issue, and few are going to want to be accused of being soft on genocidal dictators during the next campaign.