Democratic presidential hopefuls like Elizabeth Warren have started talking openly about ending the Senate filibuster. But so far, Sen. Bernie Sanders hasn’t been on board. Back in February, he said he “wasn’t crazy” about the idea of nixing the rule, which effectively requires 60 votes to pass most major legislation.

This is a bit odd, for a couple reasons. Given that there is basically zero chance Democrats will hold 60 Senate seats in the Senate in 2021, keeping the filibuster in place would almost certainly make it impossible for a President Sanders to pass many of the big ticket items on his agenda—especially Medicare for All. Second, Sanders has in the past been a vocal proponent of reforming the filibuster. Back in 2013, when some Senate Democrats pushed to weaken the threshold, he was a big supporter of forcing senators to actually stand on the floor and talk, Mr. Smith Goes to Washington-style, if they wanted to stall a bill. He understands that something is wrong with Congress’s procedural status quo.

In an interview published Monday, HuffPost’s Amanda Terkel pressed Sanders on the topic, asking how he planned to move ideas like the Green New Deal through the Senate. In response, the candidate suggested he could pass bills via the budget reconciliation process, which prevents filibusters on pieces of tax and spending legislation, allowing them to be enacted with a bare majority vote. He then reiterated that he wanted to reform, but not kill the filibuster entirely.

So we need real filibuster reform because, right now, for many many reasons, the Senate is dysfunctional. […] [T]here are ways through things like budget reconciliation—how do you think, you know, major pieces of legislation historically have been passed by 51 votes, or majority vote, through budget reconciliation. Where there’s a will, there’s a way. The problem is in terms of the filibuster, it’s an honest debate on both sides. Donald Trump supports the end of the filibuster. So you should be a little nervous if Donald Trump supports it.

Sanders added later:

I do think that every piece of legislation that I am fighting for can be passed with good legislative processes, including budget reconciliation.

Coming from another candidate, with a different to-do list, this answer might be reasonable. Reconciliation is a powerful tool that can be wielded to create or eliminate entire government programs. Bill Clinton relied on reconciliation to pass his welfare reform bill. Republicans used to it push through their tax cut in 2017. An ambitious Democratic president could probably use it to implement a carbon tax or a child allowance, expand Medicare or bulk up Obamacare.

But you know what almost certainly could not pass via reconciliation? The Medicare for All bill that Sanders has proposed. The problem is that, under the so-called “Byrd rule,” the Senate cannot use reconciliation to pass regulatory changes that only have an “incidental” impact on the budget. While the word “incidental” is open to some degree of interpretation, it’s a real limitation. When Republicans attempted to repeal Obamacare via reconciliation two years ago, the Senate parliamentarian concluded that important parts of their original bill violated the Byrd rule, such as a provision that would have locked adults out of the health insurance market for six months if they let their coverage lapse.

Sanders’ Medicare for All plan would likely have trouble making it through reconciliation because it effectively bans comprehensive private insurance. That’s arguably the defining aspect of his proposal, the thing that makes it a true single-payer system, and it would almost certainly violate the Byrd rule’s restrictions on regulations that only have an “incidental” budget impact.

Using reconciliation would also make it more challenging to finance Medicare for All, since under the Byrd Rule, legislation cannot raise the deficit outside the official budget window. There are ways Democrats could try to get around that limitation—they could pass a 30 or 40 year budget resolution, for instance—but chances are, any health care bill passed via reconciliation would either have to be paid for in full, or designed to expire within a decade (much the way pieces of the GOP’s tax bill are set to sunset).

Sanders is not the only Democrat whose agenda could be tripped up by the filibuster. Any candidate serious about passing voting rights, criminal justice, antitrust, or immigration reform would run right into it. It’s also worth remembering that, in the end, the president has no actual say over whether the Senate keeps the threshold in place; it’s up to the Senate, and the Senate only. But given that Medicare for All is his marquee proposal, and that the senator currently says he’d reject more moderate compromises, it’s especially odd that he’s still talking about keeping the filibuster around. Perhaps he thinks that by forcing Republicans to actually talk on the floor, he can neuter the rule without eliminating it entirely. But even that strategy seems a bit like magical thinking. As former Iowa Sen. Tom Harkin said back in 2013, a determined GOP could keep a talking filibuster alive indefinitely without too much of a problem, and more or less shut down the whole Senate in the process.

The minority could say, Well, we’ll take that first bill you come out here with, and we’re going to show you. If there’s forty-five Republicans and they begin to speak around the clock, let’s say they take two-hour intervals, which is not a heavy lift, each member only has to speak once every four days. They could plug the place up for two or three or four weeks. Nothing would happen.

It is also, of course, possible that Sanders realizes his agenda would require putting the filibuster to bed for good, but doesn’t want to acknowledge it yet. In his interview with HuffPost, he at least admitted that there was an argument for nixing the rule:

The problem, though, that I believe, is whether you’re in the majority or the minority, I think you have to protect minority rights. I don’t think you can just simply shove everything through. There’s an argument for that, by the way, but that’s not where I am right now.

He’s not there right now. Maybe he’ll get there later.