This has been updated.

For all of the talk about the bipartisan nature of the infrastructure bill (including by me here on The Fix), almost immediately after it passed the Senate Tuesday, Democrats did an about-face and pushed a partisan bill on their own.

Which raises the question: Why even try to do something bipartisan in the first place? Democrats control a majority in Congress and are planning to use that majority to approve $3.5 trillion more in spending in a dramatic effort to expand government more in line with how liberals such as Sen. Bernie Sanders (I-Vt.) want to see it function. Moments after the infrastructure legislation passed Tuesday, Democrats opened debate on the $3.5 trillion budget resolution and approved it early Wednesday morning without any Republican support.

The $1.2 trillion infrastructure legislation is more muted (some liberal critics say watered down) than what President Biden wanted. It sticks closely to the traditional definition of infrastructure, such as rebuilding roads and bridges and replacing lead pipes, than Republicans demanded. (Though there are also resources for expanding broadband connectivity, a major issue in rural America, and for building electric charging stations on American highways, a major goal in liberal America.)

Weeks of intense negotiating on this, including by the president, peeled off 19 out of 50 Senate Republicans and will likely win over zero House Republicans. It’s also greeted with skepticism by House Democrats. Speaker Nancy Pelosi (D-Calif.) has said she won’t put the infrastructure bill up for a vote until the House votes on the Democrats’ budget, a way to demonstrate to the base their priorities.

But Biden and Democratic leaders calculated that a bipartisan deal was a good political move as Democrats try to keep their slim majorities in Congress. Those battles will be won and lost in more moderate congressional districts and states, where voters presumably like the notion of Democrats working with Republicans. (Moderate Republicans who vote for the infrastructure bill can say the same thing.)

From a policy perspective, there is a lot that Democrats want to do with their tenuous, perhaps brief, control of Washington, and only so much they can do on their own.

Senate Minority Leader Mitch McConnell (R-Ky.), who supports the bipartisan infrastructure bill, said Republicans are “100 percent” focused on fighting the rest of Biden’s agenda. Senate Republicans can and have been doing that by filibustering Democratic legislation, so that it takes 60 votes to pass something. Senate Democrats only have 50 votes at best.

Democrats have one trick to dodge the filibuster on legislation. They can package their ideas into a spending bill that can’t be filibustered under a process known as reconciliation. But even members of their own party object to piling everything into one massive bill. It’s just too big and expensive, and some worry it would give Republicans an opening to reuse their potent “socialist” attack from 2020 against Democrats. Plus, not everything infrastructure-related would fit the specific constraints of reconciliation.

So Democrats chose to divide and conquer by attempting to get infrastructure done with the help of Republicans and go their own way for the rest. Infrastructure was the most obvious policy to break off, since President Donald Trump had spent pretty much his whole presidency proposing an infrastructure package, too.

But there are risks to the two-track path they have chosen.

The big one is that Democrats risk drowning out their bipartisan win by going big on their own right afterward.

The bipartisan infrastructure bill hadn’t even passed Tuesday, and a number of Senate Republicans were attacking Democrats for how much they plan to spend next. They’re quickly trying to tie the whole Democratic Party to the more polarizing members of the Democratic caucus, such as Rep. Alexandria Ocasio-Cortez (D-N.Y.). Trump and congressional Republicans rather successfully weaponized her Green New Deal in previous elections.

Senate Minority Leader Mitch McConnell (R-Ky.) on Aug. 10 said the budget resolution is like handing “the Squad a pen and piece of paper.” (The Washington Post)

Democrats hope that remaking government with a more liberal eye will be popular with voters. And they have reason to. A coronavirus relief package they passed over Republican objections earlier this year is popular, according to a recent Monmouth University poll. And Biden’s proposals to expand access to health care and college, which will be in the spending bill, are also supported by 63 percent of Americans, the poll found.

There’s a small — perhaps very small — risk that one or two moderate Democrats might not support so much spending in the bigger Democratic budget bill. And that would tank the proposal in the Senate. Sen. Kyrsten Sinema (D-Ariz.) said she supports “many of the goals in this proposal” but not the cost of $3.5 trillion. (The way this budget process works is that first Democrats will approve the budget outline, then they’ll spend the next few weeks actually putting money to their priorities.) Sen. Joe Manchin (D-W. Va.) expressed similar reservations as he voted for it.

Still, it’s hard to any Democrat opposing their party’s major legislative priority. Biden is relatively popular on the campaign trail, and they’d be denying him and their party a huge win.

It’s a political whiplash, to move from a bipartisan infrastructure bill to a massively partisan budget bill. And it carries with it political and procedural risks. But Democrats have calculated it’s worth it.