For months, it has been clear that President Biden, once a staid defender of the at-times-arduous and long legislative process, has grown impatient with it. As a Democratic president with a pair of effective Democratic majorities in Congress, he sees this moment as the time to get big things done. But that same staid process he has often — including very recently — defended now poses his biggest hurdle, particularly given how slim Democrats’ majorities are.

On Tuesday, he offered perhaps his most forceful — yet still subtle — suggestion that Washington should change how it does business.

At an event in Tulsa commemorating the 100th anniversary of the massacre there, Biden spotlighted the hurdles to his agenda. In doing so, he turned attention to members of his own party.

“I hear all the folks on TV saying, ‘Why doesn’t Biden get this done?’ Well, because Biden only has a majority of effectively four votes in the House and a tie in the Senate, with two members of the Senate who vote more with my Republican friends,” he said. “But we’re not giving up.”

It wasn’t at all difficult to parse which two Democratic senators Biden had in mind: Joe Manchin III (D-W.Va.) and Kyrsten Sinema (D-Ariz.). Perhaps Biden was indeed just being defensive about why he may not be able to get more done, but you could certainly be forgiven for thinking he chose to highlight those two senators in an effort to apply pressure on them.

But pressure for what?

Plenty of fact-checkers quickly noted a supposed problem with the argument. In fact, Manchin and Sinema have voted with Biden 100 percent of the time on big bills, according to FiveThirtyEight vote rankings.

But Biden’s argument wasn’t necessarily about that. And if you look at voting records over the past four years, he’s right to spotlight Manchin and Sinema. Among Democratic senators between early 2017 and early 2021, they voted with President Donald Trump more than any of their sitting Senate colleagues. Sinema’s record in particular, when you factor in the political lean of her constituency, skewed more toward Trump than any of her Democratic colleagues.

Manchin and Sinema haven’t been forced into a position in which they had to vote against the Democratic president on big bills. But their presence in a 50-50 Senate, no question, makes it more difficult to pass Biden’s agenda. Even the prospect of their “no” votes can mean legislation never actually comes to a vote.

As The Washington Post’s Sean Sullivan and Mike DeBonis wrote Tuesday, Manchin in particular is facing lots of party pressure to support Democrats’ voting rights bill. There are fears that if the senator from the second-Trumpiest state in the 2020 election strays from the party on voting rights, he could also torpedo future legislation on things such as climate change, gun control and immigration.

But it is Manchin’s and Sinema’s shared stance against reforming the Senate’s filibuster rules that poses the biggest roadblock to Biden’s agenda.

The effective 60-vote threshold the filibuster creates for most legislation means there’s a premium on Democratic unity to, at the very least, pressure Republicans to negotiate. It’s very doubtful Republicans will suddenly warm to bipartisanship, given the example of the past decade-plus, but you can’t really press that issue if you can’t even win the votes of your own senators.

What’s perhaps most interesting to me about all this, though, is what it says about Biden and his approach.

There’s another guy who has supported maintaining the filibuster in the relatively recent past: Biden. The president defended the filibuster as recently as the 2020 campaign, but he has since gradually moved toward supporting a potential change, suggesting support for restoring the “talking filibuster” and possibly going even further than that.

But to make any changes, he needs all 50 Democratic senators to go along, including Manchin and Sinema.

Again, it’s possible that Biden’s comments on Tuesday were simply defensive when it comes to what lies ahead and the possibility that his agenda will go no further. But he’s also extremely studied in the ways of Washington, in which everyone knows calling out allies is dicey. He had to know that not terribly subtly spotlighting Manchin and Sinema would be viewed as provocative.

The potential downside is that you alienate those you depend upon. Manchin, in particular, has plenty of incentive not to align with Democrats’ agenda. (Indeed, you could certainly argue that Democrats should be happy to have a senator from deep-red West Virginia voting with them on much of anything.) Sinema has also proved rather strong-willed in the face of lots of pressure for her to fall in line and criticism from liberals on things such as voting against an amendment to increase the minimum wage to $15 per hour. (Her objection wasn’t to the increase, but rather it being included in a coronavirus relief package.)

Manchin’s and Sinema’s offices declined to comment on Biden’s remarks.

If we’re reading into Biden’s comments on Tuesday, it’s that he recognizes his agenda goes nowhere without keeping the troops in line — and the possibility it completely stalls is very real. It also seems to be the latest iteration in his gradual warming to changing filibuster rules which, after all, is mostly what Manchin and Sinema are standing in the way of.

Keep an eye on whether he keeps it up; that will be the surest sign that he’s moving toward going nuclear.