Congress has enormous power over all kinds of things but only if they actually want to use it. But over the years, Congress has shown very little interest in constraining presidential warmaking power. At times presidents have shown interest in demanding that congress vote on their war proposals—like when George W Bush forced a vote on invading Iraq timed right before the 2002 midterms but months before he initiated military action—but that’s something initiated by the White House for political purposes. For most of the same reasons, members prefer to duck votes on these things when possible.
Of course, I'm with Conor. The war in Libya becomes illegal from now on. And the imperial presidency grows even more powerful.