So the Blunt amendment was just defeated in the Senate by a vote of 51-48. Only one Republican voted against it, while three Democrats defected from their party leadership and supported the measure.

Now the fight really starts.

Democrats have virtually the entire Senate GOP caucus on record supporting a measure that would allow employers and insurers to deny coverage of any health service they deem morally objectionable.

They view this as a potent issue among independent and/or unmarried women in key swing states — in both the Senate and presidential races. Mitt Romney fully embraced the Blunt amendment in interviews yesterday and today.

But the key is to understand how Dems plan to use it.

The GOP views this as a way to advance a key storyline about Dems — that they are so ideologically committed to expanding government power that they even want it to reach into matters of faith. But Democratic operatives believe that the specter of intrusive government can actually cut in their favor in this debate.

They believe that independent voters — particularly women — are prone to see this as a bid by elected officials to dictate that their employers’ values should be able to trump their own values. Dems believe independents will see the bid to empower employers not to cover contraception as a heavy-handed infringment on their freedom.

Republicans, of course, will scoff at this, arguing that the government is mandating that insurers cover services that employers object to — and will ultimately have to pay for. But Dems believe public attitudes towards contraception are so liberal that they will color perceptions of this whole debate and make the public more receptive to the Dem framing of it — inevitably making the GOP framing look hidebound and reactionary.

A national Dem operative tells me paid ads on this issue is a real possibility in swing states like Virginia, Ohio, and Nevada. It’s already a major issue in Massachusetts; Scott Brown voted for Blunt today. Republicans think Dems in states like Nebraska, Montana, and Missouri embrace this at their peril.

Now it’s true that too many Dems defected on this issue — Senators Ben Nelson, Joe Manchin and Bob Casey voted for Blunt. And it’s true that the expected defections among Republicans didn’t materialize. Both Susan Collins and Dean Heller voted for it — the latter vote being particularly interesting, since he’s already under fire in the Nevada Senate race for his opposition to Planned Parenthood.

The lack of GOP defections could either signal that Republicans don’t believe this is the loser Dems say it is, or that Republicans decided their best hope was to hang together and hope for the best. Either way, both sides have laid their bets, and given the commitment of base voters on either side to this issue, this battle isn’t going away.