As the Senate moves towards a vote on Harry Reid’s gun violence package, which now (after the excision of a renewed assault gun ban and high-capacity ammo clip restrictions) centers on a quasi-universal background check system for gun sales, there are a lot of shifting techtonics to keep in mind:

First, public opinion remains overwhelmingly in favor of universal background checks across just about every subset of the population. The opposition may be noisy and influential, and benefits from the perception that this is a “voting issue” only for opponents, but this is at present not a close call in terms of where the public stands.

Second, the near-unanimity of public opinion probably reflects the ironic fact that for many years a stronger background check system was the default-drive alternative offered by the NRA to every other gun measure. Yes, the gun lobby has been fighting to protect the “gun show loophole” to background checks for some time, and has quietly worked to undermine the system as it exists, but it’s still difficult for Lapierre and company to pretend it represents a deadly threat to the Second Amendment.

Third, we are in a period where the once-powerful force of red-state Democratic reluctance to make waves on “cultural issues” is waning. There are fewer red-state Dems to worry about, for one thing. For another, voter polarization and reduced ticket-splitting have made the route to survival for red- (and more often, purple-) state Democrats depend more on base mobilization than has been the case in the past.

This last factor remains important in the 60-vote Senate, however. Plum Line’s Greg Sargent runs the numbers this morning, and identifies five Democrats and three Republicans who are being cross-pressured by the usual NRA threats–but also by Michael Bloomberg’s lavishly funded upcoming ad campaign pushing back.

How individual senators, the two parties, and the White House calculate all these factors will largely determine what happens after the Easter Recess. But in this installment of the Gun Wars, it’s no longer quite the simple question of doing what’s right versus doing what’s expedient that it used to be.

Ed Kilgore

Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.