As they threaten to stage a rare filibuster of Neil Gorsuch, President Trump's Supreme Court pick, Senate Democrats are essentially daring Senate Republicans to do what they stopped short of doing a few years ago: getting rid of the minority party's centuries-old ability to filibuster all nominees.

"When Democrats were in charge, we were concerned, well, what if Republicans are in charge? Let's keep that 60-vote threshold in place," Sen. Amy Klobuchar (D-Minn.) said on ABC.

Republicans are trying to point the finger right back. "I would say that is up to our Democratic friends," Senate Majority Leader Mitch McConnell (R-Ky.) said Sunday on CNN.

I called up someone who was in the thick of the Democrats' decision to get rid of the minority party's ability to block most of a president's political and judicial nominations for a behind-the-scenes look at why Democrats saved the filibuster for Supreme Court nominees -- and who might be blamed for undoing it in the next few months. (Although no matter what happens, senators can still filibuster legislation.)

Brian Fallon was the communications director at the time for Sen. Charles E. Schumer (N.Y.), who is now the top Senate Democrat. (Fallon was also the national press secretary for Hillary Clinton's 2016 presidential campaign.) We spoke in January before Trump had nominated his Supreme Court pick, and our answers have been edited for length and clarity.

THE FIX: What exactly did Democrats do when they blew up the filibuster in 2013?

Then-Senate Majority Leader Harry M. Reid (D-Nev.) speaks at a news conference in 2013 after Senate Democrats voted to get rid of the filibuster for most nominations. (Chip Somodevilla/Getty Images)

So there were two thresholds that were crossed: Number 1, it set a precedent for changing the rules of the Senate by a simple majority vote [as opposed to the theory advanced by some that it took a two-thirds vote to require a rule change].

And then the second threshold that was crossed was: Now that you can change the rules by a simple majority, what should you change the rules on? Senate Democrats said: "We actually like the idea of a higher threshold for something as important as the Supreme Court. And we do think the Senate should continue to play a role for having higher standards [than the House] for passage of legislation. So we're not going to disturb the filibuster in those two places. But for Cabinet-level appointees and for sub-Supreme Court judicial nominations, a simple majority should suffice."

THE FIX: In retrospect, you could argue that getting rid of the filibuster has backfired on Democrats -- just look at Trump's very conservative Cabinet nominees.

I think you heard Democrats, from Sen. Chris Coons [D-Del.] to Schumer himself, saying that given the situation they find themselves in, they do regret the decision to change the rules.

That was not something that was undertaken lightly. The rules change, when it happened, followed two to three years of agitating by some of the chamber's younger members, some of whom had been elected in an era where Democrats were approaching a 60-vote majority and didn't yet know life in the minority. Schumer was among those who actually tried to stave off the push to change the rules.

Senate Majority Leader Mitch McConnell, left, walks through the Capitol with then-Vice President-elect Mike Pence in November. (Bill O'Leary/The Washington Post)

THE FIX: If Republicans do go nuclear, they will most certainly attempt to lay the blame at Democrats' feet for blocking Judge Neil Gorsuch in the first place. What might Democrats say back?

Well, McConnell will have to take a new, affirmative step for him to utilize the very same mechanisms he criticized -- for a purpose and utility that Senate Democrats showed discretion about no less.

That would uniquely make him the owner of that step. He could not say, "Harry Reid did this." He would supplant Reid in that instance as somebody that was actively diluting the filibuster.

THE FIX: So you're saying undoing the filibuster for all nominees will be on Republicans' hands?

There will literally be a moment in the Senate where there will be a vote [to undo the filibuster], and it will be a major vote. It will probably be one of those things that's important enough where senators are seated in their desks and the cable news might take it live, too, and it will be an undeniable moment in time where a new step is being taken. So at that point, it will be hard for anybody to argue [Republicans] are not doing something new and drastic.