There's a wild card that applies to all discussion of what happens next: the possibility that Gov. Chris Christie will appoint an interim senator over the short term. If that person is a Republican (which he or she almost certainly would be), the new senator would be representing a heavily Democratic state, and might be willing to echo Lautenberg's vote on some issues, like, potentially, new gun control measures.
The "nuclear option" on filibusters
Effect of Lautenberg's death: Very high
As we noted last week, Reid and the White House wanted to use presidential appointments to fill vacant Appeals Court positions as an opportunity to revamp rules on filibusters. Right now, such appointments — once considered fairly routine — are regularly blocked, which has led to a three-person vacancy on the D.C. Circuit Court of Appeals. By nominating three people at once, the idea seemed to be, Senate Republicans could be forced to either hold a vote on one or two of the candidates, or demonstrate that the filibuster for appointments should be revised.
Such a revision would take only a simple majority vote in the Senate. But Reid was already toeing that line prior to Lautenberg's death. According to sources doing the counting, Reid could rely on 51 votes as of last week. Now, he's at 50. Three scenarios emerge:
The Senate remains as is. Right now, the Democrats hold a 52 to 45 advantage, with two independents who generally vote Democratic. If last week's count is correct, a vote held today would be, at worst, 50-49 — enough for passage.
Reid loses another vote. If Reid loses another vote, that calculus shifts. Last week, a senator deciding against changing the filibuster rules would have spurred a tie in the Senate — moving the tally to 50-50, and meaning that Vice President Biden could break the tie. If Reid loses that vote now, though, it flips to 49-50, and Biden isn't needed.
Christie appoints an interim senator. If Christie appoints an interim senator, Reid can consider that vote lost. There's very, very little chance that Christie wouldn't appoint a Republican, and there is basically zero chance that a Republican would back a plan giving the Democrats the ability to rubber-stamp appointments. In other words, a Christie appointment means that Reid may have to rely on Biden to break the tie by default — which it's not clear the White House would want to do.
Effect of Lautenberg's death: Low
Last month, a bipartisan group of eight senators developed — and the Senate Judiciary committee approved — a proposal that will significantly revamp the rules around immigration. But, rather weirdly, the backers of the bill want to push to see that it gets 70 votes in the Senate. "Our goal is to get 70 votes. It is going to take a lot of work," Senator Chuck Schumer told Politico. It suggests that perhaps the group heard that the new filibuster-mandated 60-vote standard for approval was off by ten, but interpreted it in the wrong direction.