With the magnitude of yesterday’s victory in the presidential race beginning to sink in, it’s worth pausing to note what a huge deal it is that Democrats, unexpectedly, gained seats in the Senate — and even more to the point, that the influx of new arrivals means a more liberal and energetic Democratic caucus.

This could matter when it comes to some of the most important battles set to unfold in Congress: Over tax hikes on the rich; entitlements; and perhaps even immigration reform.

With the news breaking just now that independent Angus King of Maine is likely to caucus with Dems, that means the party has expanded its majority to at least 55 seats. But as David Dayen notes, yesterday’s Senate victories were not just partisan; they were ideological:

Elizabeth Warren and Joe Donnelly and Angus King picked up seats, and all of them are to the left of what is currently in that seat on most issues, to varying degrees (obviously Warren is significantly more liberal, while the other two more in the sense that they don’t have the pressures of voting with an obstructionist minority). But there’s more. Chris Murphy is well to the left of Joe Lieberman, enough that you could call that a pickup in itself. Tammy Baldwin is way to the left of Herb Kohl. Martin Heinrich is probably a little to the left of Jeff Bingaman. Heidi Heitkamp is probably a wash with Kent Conrad. And a number of the incumbents are free to vote a bit differently given that they won’t be up for re-election for 6 years.

It’s going to be very interesting to see how this shifts the dynamic. As I noted here recently, many of the new arrivals have already pledged to back filibuster reform.

Meanwhile, Congressional expert Norm Ornstein tells me that the shift leftward could have an impact on how the Dem caucus ultimately handles Medicaid. As Digby noted recently, there’s reason to worry about the possibility that Dems might acquiesce to serious Medicaid cuts during upcoming deficit reduction negotiations. But Ornstein says liberals in the Senate might push back and make that less likely.

“Having a liberal Senate means you’re going to do less onerous things to the elderly the poor and the disabled,” Ornstein says. He also thinks immigration reform is a real possibility, because there are going to be a “significant number of Republicans who know their party’s dead without it.” The details of immigration reform, he says, could be “shaped a bit by having more liberals.”

And finally, there’s taxes. As Dayen notes, the imminent influx of progressives suggests there’s good reason for Dems to simply let all the Bush tax cuts expire, and then, when the liberals arrive next year, pass Democratic tax cuts for the middle class.

After all, there are no signs that yesterday’s results are getting Republicans to rethink their opposition to tax hikes on the rich — or their designs on entitlements. Did you catch this quote from Grover Norquist?

The election did solidify one thing. The modern Republican party is the party of the Ryan Plan: No tax hikes, Reaganesque tax reform, and entitlement reform.

And Paul Ryan is returning as the House GOP’s budget chief. We’re going to need more solid progressives in the Senate next year.


UPDATE: Steve Benen also raises a good point: If this is going to matter, Democrats very likely will have to pursue filibuster reform, so it’s a good thing the new arrivals are committed to it.