Last night at 11:20 pm, a colleague texted, "We still have the filibuster, right?"

My answer: "For now."

Quick background: On November 21, 2013, a frustrated Democratic majority "reinterpreted" the Senate's cloture rule so a simple majority (instead of three-fifths) could limit debate on all judicial and executive branch nominations except Supreme Court nominations. As I noted at the time, this was an "especially bold" approach since they reinterpreted rule so that "three-fifths" means "simple majority," math notwithstanding.

As of today, Supreme Court nominations and most legislation is still subject to filibustering. There are exceptions: Over the years, Congress has enacted laws exempting some legislative proposals, like budget resolutions and reconciliation bills, from obstruction. But the "right" to filibuster is fragile: It has never been affirmed in the rules of the Senate, it has always been subject to limitation by precedent, and the 2013 precedent highlighted how easy it is to restrict or eliminate the right.

So what happens next? After Tuesday's results, the reader will understand if I am shy about making predictions. Instead, here are four scenarios:

1) Senate business as usual: Republicans bring up the Trump-Republican agenda on the floor, and Democrats block their bills or hold out for modifications in the bill or the right to offer amendments on other issues. Some bills fail, Trump activists complain, and Republican senators shrug and say, "Sorry, that's how the Senate works."

2) Ex ante compromise: Senate Majority Leader Mitch McConnell (R-KY) and Senate Minority Leader Charles Schumer (D-NY) agree on a set of incremental reforms — perhaps cosmetic, maybe substantial — at the start of the 115th Congress with the understanding that the issue of reforming the filibuster is off the table for the rest of the Congress.

3) Planning to fail: Many Senate Republicans are now in the awkward position of advancing an agenda they may oppose for a president they know is reprehensible. If they refuse to vote for Trump's agenda, they face a backlash from the Trump base. Sure, they could actually be honest and open about their reservations, but most of them have been cowards up to this point, and it is possible they will continue this course.

Allowing the Democrats to filibuster helps get them out of this bind. A conscientious-objector Republican can bring up a bill to say, build a wall along the Mexican border, let the Democrats block it, and then either give up on the bill or weaken it until it is a fraction of its original form.

The challenge of this approach is avoiding the howls of outraged Trump activists and media allies calling for...

4) Ex post reform: Just as the Democrats demonstrated that any day is a good day to reform the filibuster, Republicans inside and outside the Senate who actually want to see the Trump agenda pass and then see it blocked by a filibuster may call for its swift and immediate demise when Democrats block the Republicans' bills. As in previous cycles, the members of the majority will be called upon by the party base to vote for reform, and the critical question is whether enough Republican senators would balk to keep the filibuster alive.