Senate Democrats are going to hold a vote today on the GOP budget plan that includes the proposal to end Medicare as we know it, in an effort to put Senate Republicans on the spot and keep up momentum after the big Dem victory in NY-26.

Here’s what Dems will be watching for: They will be looking in particular at how Senate Republicans who previously declared support for the Ryan plan vote today. The idea is that if Republicans switch their position and vote No, it will reinforce a sense that Republicans have concluded that their loss in NY-26 signals that this special election is a bellwether of sorts and that the Ryan plan is­­ increasingly toxic in other parts of the country.

Meanwhile, if Senate GOPers don’t switch in substantial numbers, Dems will point to it as proof that Republicans aren’t listening to the American people and can’t dump the Ryan plan because the GOP base won’t let them.

The idea behind moving so quickly to hold this vote is that Dems want to reinforce the storyline that came out of last night’s results — that Republicans are on the defensive and that the GOP Medicare plan is forcing GOPers to choose between their base and the American mainstream.

The idea is also to try to create a rift between House and Senate Republicans. Here, for instance, is Paul Ryan on MSNBC this morning, insisting despite last night’s results that House Republicans remain united behind the plan:

It’s actually true that House Repubilcans remain united behind Ryancare: Few if any House GOPers have broken with the plan. And if Senate Republicans do break with it today, Dems will point to it as proof of GOP divisions over the issue.