By the end of the day Thursday, one major use for the filibuster is likely to meet its death. Republicans plan to get rid of senators' centuries-old ability to filibuster Supreme Court nominees. The historic move would override a Democratic filibuster to put the GOP's guy in a Supreme Court seat that has been vacant for 419 days.

But the man who will pull the trigger on the filibuster — Senate Majority Leader Mitch McConnell (R-Ky.) — has promised he'll save one very important aspect of it: its use to block legislation.

Ironically for Senate Republicans, keeping that part of the filibuster intact could ensure that Judge Neil Gorsuch's confirmation to the Supreme Court would be the only major victory they could bank on.

As Thursday's rare blockade of Gorsuch underscores, Senate Democrats are willing to go to war to block President Trump's agenda. And McConnell is leaving them one very critical weapon — a 60-vote threshold (or three-fifths of the Senate) to pass any legislation Democrats don't like.

Senate Republicans don't control three-fifths of the Senate. They have 52 members, and they haven't been able to reliably count on the 10 Trump-state Democrats up for reelection in 2018 to cross party lines on high-profile partisan battles. (Just three of those Democrats won't support their party's filibuster of Gorsuch.)

Which means it's very likely that for the next 1 ½ years of this Congress, Democrats will have the power to hold up most major pieces of legislation Republicans want to undertake. We're talking tax reform, health-care reform, infrastructure reform, defunding Planned Parenthood; you name it, Democrats could conceivably block it. (There are imperfect ways around the filibuster, which I explain here and here.)

What's more, after Republicans override their filibuster on Gorsuch, you could argue that Democrats will be even more motivated to block anything else Republicans want to do.

Talking to reporters this week, McConnell acknowledged the irony of all this.

“Who would be the biggest beneficiary of that right now? It would be the majority, right?” he said of getting rid of the filibuster for legislation.

But, he pointed out, virtually no GOP senators are calling for the demise of the filibuster for legislation.

“There’s not a single senator in the majority who thinks we ought to change the legislative filibuster,” McConnell said. “Not one.”

Nor are there many Democrats who want to see it go. The filibuster is the Senate's most defining feature. It allows any member of the 100-member chamber to hold up legislation she or he doesn't agree with, and it requires three-fifths of the Senate to reach a consensus to move forward. By contrast, in the House, what the majority wants, the majority gets.

“Things should require more consensus,” Sen. Mazie Hirono (D-Hawaii) said on NPR recently, echoing the value senators on both sides of the aisle put on the filibuster. " … It is because of the 60-vote requirement that requires us to talk to each other, to be much more attuned to other perspectives.”

Plus, most senators are pretty used to partisan gridlock created by the filibuster. The tactic has been a headache for the majority party for more than a century, writes Cornell Law Professor Josh Chafetz.

When Democrats were in power during the Obama administration, then-Senate Majority Leader Harry M. Reid (Nev.) got so fed up with Republicans' filibuster of three of President Barack Obama's U.S. Court of Appeals nominees that he ended the filibuster for all non-Supreme Court picks. It's a mirror situation (if not somewhat escalated) now that Republicans are in power.

On the filibuster for nominees, McConnell has calculated that the cost (doing something that his party cried bloody murder on when Democrats did it) is worth the benefit (replacing a conservative on the court with a conservative). But he doesn't think the benefit of having an ability to pass whatever legislation his party wants is worth the cost of undoing the filibuster further.

Molly Reynolds, a congressional analyst with the Brookings Institution, points out that in some cases, Democrats could be doing McConnell a favor by holding up legislation.

“There may well be situations that arise where having the filibuster will provide McConnell cover, allowing him to blame the rule for things that may anger some Republicans but may ultimately be better for the party,” she said. If the Senate had voted on Republicans' troubled health-care bill in March, for example, they would have done it under a process that let them skip a filibuster. And McConnell would have had no one to blame if the bill failed — or, worse, if it passed and was unpopular.

When Reid undid the filibuster for lower-court nominees in 2013, virtually everyone in Washington predicted the filibuster for Supreme Court nominees was on its deathbed. It's tough to predict what the future of the filibuster for legislation will be, but for now, it seems to be safe in Republicans' hands — even if it comes at their own detriment.