C'mon, cyphen, don't pretend to be naive. That rider was slipped into an appropriation bill that practically nobody had read in its entirety. Even if the Democrats had wanted to amend the bill to remove this crap, the Republican leadership wouldn't have allowed a vote on the merits. It was $20 million out of about $300 billion, and withholding approval of the overall bill would have had the Republicans screaming "Support the troops!" So, yes, they voted for it, and no, they weren't happy about it.
Be realistic: polls or no polls, there's an election coming up. The Republicans are doing their level best to commit suicide. Why should the Democrats say, "Excuse me, but may we borrow your rope for a minute?"