As it becomes increasingly clear that a bipartisan group of senators might reach a deal on an infrastructure package, this is giving rise to thorny procedural dilemmas for Democrats.

As always, those dilemmas trace back to a perennial challenge of our age: how to deal with the bad faith of Republicans.

The key question is this: If such a bipartisan measure does pass, how can progressives be certain a second package containing their priorities will ever pass via a simple-majority reconciliation vote?

And if progressives cannot be certain of this, then shouldn’t they withhold their support for the bipartisan package until they can get a guarantee that the second one will pass?

Politico reports on two new developments on this front. First, the bipartisan deal is getting closer to fruition: The latest version would total over $1 trillion in spending, mostly on roads, bridges and other infrastructure spending Republicans can support, though only about $579 billion of it would be new spending.

There’s still no clarity around how it would be paid for — Democrats oppose a hike in the gas tax and user fees, and Republicans oppose higher corporate tax rates — but a deal is at least possible.

Second, Politico reports, White House advisers are privately assuring progressives that they needn’t worry, that they are fully committed to a second package by reconciliation.

Right now, the Senate Budget Committee — chaired by Bernie Sanders, a Vermont independent — is drawing up the vehicle for a multi-trillion-dollar reconciliation measure. If a bipartisan deal on bricks-and-mortar infrastructure is reached, that reconciliation vehicle can be used to pass the rest of President Biden’s infrastructure and jobs plan, such as funding for child and family supports and for our caregiving infrastructure. If no bipartisan deal is reached, Democrats can do the entire package via reconciliation.

But progressives fear that if a bipartisan deal does happen, there’s no assurance that moderates such as Sen. Joe Manchin III (D-W.Va.) will back the reconciliation package. As Sen. Edward J. Markey (D-Mass.) said on NBC, progressives must insist on a “procedural guarantee” that both would pass together. If not, they should oppose the bipartisan package, possibly killing it.

To deal with these progressive worries, White House strategists are privately telling progressives that they’re fully committed to that second reconciliation vote. But this isn’t a guarantee that locks in the support of moderates like Manchin.

The problem is that Democrats fear such a procedural guarantee might give Republicans a way to walk away from the bipartisan deal, which Biden appears to badly want. They might argue there’s no reason to support it if Democrats will then raise corporate taxes for large public expenditures on liberal priorities by themselves.

But Democrats cannot let such a fear set the agenda. If Republicans do end up doing this, then they were never operating in good faith, and never intended to reach a bipartisan deal in the first place.

We’re already seeing this bad faith surface. Sen. Joni Ernst (R-Iowa) recently tried to argue that the mere fact that Democrats are talking about reconciliation at all somehow proves Biden “really doesn’t want to do a bipartisan deal,” because this makes Republicans “upset.”

That’s absurd on its face. As Steve Benen aptly responded:

Remind me: when was the last time Ernst’s Senate Republican caucus based its legislative strategies on whether it might make Democrats “upset”?

Exactly right. And Democrats can’t let this sort of nonsense shape their strategy.

“Republicans either want to pass these policies on the merits, or they view this as a way to undermine the rest of Biden’s agenda,” Jesse Lee, the vice president of communications at the Center for American Progress Action Fund, told me. “If Republicans aren’t acting in good faith, let them put their cards on the table.”

That means locking in a guarantee that moderates will back a reconciliation bill later. Ilya Sheyman of Real Recovery Now, a coalition of labor and lefty groups, tells me Democrats should focus, first and foremost, on uniting around “a reconciliation package of sufficient scope and scale.”

After that, Sheyman says, it won’t be hard to fix on a procedural way to “ensure that passes in advance of any narrow bipartisan agreement around roads and bridges.”

For instance, Rep. Alexandria Ocasio-Cortez (D-N.Y.) has suggested that House Democrats can simply hold off on passing any bipartisan bill the Senate completes until the Senate then passes the reconciliation one as well. Then the House can pass both.

In the end, a key goal of these bipartisan talks is to give Manchin and moderates cover to support a robust reconciliation bill, whether it’s after a bipartisan bill passes or after the bipartisan talks fail. And that’s fine. Democrats must do what they must to win Manchin and company.

But fear of upending those negotiations can’t then be allowed to imperil the process of guaranteeing that the reconciliation bill will pass later. Republican bad faith can’t be allowed to set the agenda.