On a conference call just now, Senator Chuck Schumer confirmed it: Senate Democrats will continue bringing up the Buffett Rule again and again in an effort to put Republicans on the spot, and he vowed Dems would press the issue until Republican opposition cracks.

Tellingly, Schumer also noted that Mitt Romney personally benefits from the current tax code that the Buffett rule would undo — and that this would make it politically harder for GOPers to maintain opposition. This confirms what I’d been saying: The Buffett Rule is partly about forcing Republicans to take a stand on whether the likely GOP nominee — who is worth $250 million — should pay lower tax rates than many middle class taxpayers do.

Sheldon Whitehouse’s Buffett Rule proposal is set for a vote on April 16th, but Schumer said this is just the beginning.

“If we come up short of the 60 votes needed, we’re going to keep pushing this isue all year,” said Schumer, who’s also the Dem messaging chief. “It’s an emerging contrast with Republicans. We think the very wealthy should share in more of the sacrifice.”

Schumer noted that Romney benefits from low tax rates, and predicted Republicans — and Romney — would struggle to defend them.

“Democrats, independents, and Republicans are for implementing the Buffett Rule,” Schumer said. “Romney has benefitted from a low tax rate. Republicans will continue with cries of class warfare, but they are falling on deaf ears, because it’s the middle cass t’s under assault. If and when Romney becomes nominee they’re going to have to move in our direction more quickly than people think.”

Republicans and conservatives have scoffed at the Buffett Rule, arguing its contribution to deficit reduction would be minimal. But Schumer insisted it would bring in $160 billion over 10 years in the event the Bush tax cuts are extended, and said this is not just about deficit reduction, but about basic fairness.

“The middle class can no longer bear the burden of reducing deficits alone,” Schumer said, adding that Republicans are now “on the defensive on their signature issue.”

Dems view the Buffett Rule as a good way to make one of their most important arguments: The battle over the deficit is actually one over who should sacrifice to reduce it. Dems like this fight because they’re hoping continued GOP opposition to the Buffett Rule will starkly reveal the true nature of GOP priorities on this score to the electorate.

If anything, Schumer’s comments — along with the GOP nominee’s own wealth and tax rates — confirm yet again how central tax fairness will be to Campaign 2012.