For congressional Democrats, the road map to legislative success was relatively clear. The Senate approved a $3.5 trillion budget resolution this week with unanimous support from the Democratic conference. Once the Democratic-led House returns to work and dose the same, members can move forward with working out an ambitious intra-party compromise.

This morning, however, we learned of an unexpected wrinkle that may affect the plan. NBC News reported:

Nine House Democrats are warning Speaker Nancy Pelosi, D-Calif., that they won’t vote for a budget resolution until the House passes the bipartisan infrastructure bill advanced by the Senate this week…. The letter, dated Thursday, was led by Rep. Josh Gottheimer, D-N.J., the co-chair of the bipartisan Problem Solvers Caucus.

The New Jersey Democrat was joined by Reps. Carolyn Bourdeaux (D-Ga.), Filemon Vela (D-Texas), Jared Golden (D-Maine), Henry Cueller (D-Texas), Vicente Gonzales (D-Texas), Ed Case (D-Hawaii), Jim Costa (D-Calif.), and Kurt Schrader (D-Ore.).

To put it mildly, these moderate House Dems have a plan that is … flawed.

The process envisioned by House Democratic leaders and the vast majority of progressive members has been unchanged from the outset. The chamber will tackle the $3.5 trillion measure, and once it passes, the House can then approve the Senate’s bipartisan infrastructure legislation, sending both parts of the two-track package to the White House for President Biden’s signature.

The nine moderates are demanding to move things around: vote on the Senate’s bipartisan infrastructure bill first, and then they’ll consider the rest of the party’s plans. Maybe. If they feel like it.

If Democratic leaders fail to satisfy these nine moderates — representing roughly 4% of the House Democratic conference — they’ll derail the budget resolution and the entire White House agenda will collapse because nine members couldn’t bring themselves to support a budget resolution that even Sens. Joe Manchin (D-W.Va.) and Kyrsten Sinema (D-Ariz.) endorsed.

Or put another way, progressive Dems won’t support the bipartisan infrastructure legislation until the reconciliation bill passes, and moderate Dems won’t let the fight over reconciliation even begin until the bipartisan infrastructure legislation gets a vote.

There’s a tactical problem the moderates may not fully appreciate. Let’s say Pelosi, left in a tough spot, caves to the centrists’ demands and brings the Senate’s bipartisan infrastructure bill to the floor, just as they’re insisting. I don’t think this is likely, but just for the sake of conversation, let’s say this happens. Would the legislation pass?

Almost certainly not. The vast majority of House Republicans would oppose it, because they don’t like the bill anyway, and the vast majority of House Democrats would also oppose it, because they want to keep it on the shelf while negotiations continue on the larger and more ambitious bill. Indeed, House progressives have the leverage right now, and they wouldn’t give it up just to make nine centrists happy.

In other words, these nine moderates are effectively asking their own party colleagues, “Let us have the Senate bill, and while you’re at it, also give us the power to undermine the rest of Biden’s popular domestic agenda.”

Why would the other 211 House Democrats go along with this? They wouldn’t.

This is precisely what many progressive members were worried about, which is precisely why the moderate members’ plan will not work. The legislative arithmetic is unavoidable: the moderates need the progressives’ votes, and progressives have no incentive to go along.

Complicating matters, this nine-member faction has left itself on an unstable branch. These centrists can swallow their pride now and walk back their threat, since it’s based on a demand that won’t be met, or they can follow through, kill Biden’s domestic agenda, invite primary rivals, and destroy their party’s chances in the next round of elections.

I realize that these moderates really want to pass the Senate’s bipartisan plan. The White House and Democratic leaders want that too. But there’s one sure-fire way to guarantee its passage, and that’s to approve the party’s budget resolution and get to work on a reconciliation package.

If the moderates follow through on their threats, they’ll end up defeating the bill they want to pass. The sooner they realize this, the better it will be for everyone.