The idea is to vote on the middle class cuts, then box Republicans into calling for cuts for the rich. "Those Republicans will have to stand up and say, 'Don't forget the high earners.' They will have to call for an amendment."
Here's where it gets a little procedural. If Majority Leader Harry Reid "does it right," the aide argued, here's how the process would break down, just in time for the midterms.
According to the aide, as early as next Monday Sept. 27, the Democrats would start the debate. The aide's hypothetical looks like this:
Sept. 27 or Sept. 28: Reid brings up the bill to extend middle class.
If Republicans object, they look like they are obstructing tax breaks for every American.
If Republicans allow it to go forward, there can be a vote. If they insist on their plan to freeze tax rates at their current levels, keeping the tax cuts for the rich, they would be allowed to do so in the form of an amendment to the middle class bill.
But to pass that amendment, 19 Democrats would need to jump on board as well, taking a vote that effectively gives rich people a larger tax cut. The aide thinks that won't be happening.
This is why Minority Leader John Boehner's big reveal (and subsequent walkback) that he'd be willing to support a middle-class only plan if that were his "only option" was such a critical development.
"f they are forced into a 'will you vote for the middle class tax cuts,' they have a decision to make and a debate to have. If they don't support us they look isolated, champions of the richest of the rich," the Senate aide said. "We win with either option."
Late Update: A senior Republican leadership aide writes in to suggest that our Democratic aide is full of it since logistically not possible to get started on Monday or Tuesday given this week's agenda of the Defense Authorization bill. The Senate operates on a clock, so the earliest they could get to the tax debate would be mid-week.
The Republican is correct on the timing, so the debate would start later next week, the Democrat said. However, the Democrat confirmed to TPM what's been rumored, that Reid is highly likely to set aside the defense bill and postpone a final vote until after the election.