Democrats Ready a Tricky Legislative Two-Step. It’s Been Done Before.

Passing a far-reaching partisan social policy measure and a bipartisan infrastructure bill almost simultaneously will strain the abilities of congressional Democrats in the coming weeks, forcing them to hold their members together on complex and costly policy as they seek to thread a legislative needle.

But a similar feat was pulled off in 2010, to secure the last landmark Democratic legislation, the Affordable Care Act. Then, circumstances forced Democrats to pass the underlying legislation with a 60-vote Senate majority and an accompanying budget reconciliation bill that was filibuster-proof to complete the job. Now, completing the job means securing President Biden’s ambitious social welfare agenda.

And some of the same principals who were intimately involved then are still around, notably Speaker Nancy Pelosi and Mr. Biden.

“It’s like the 7-10 split in bowling,” Senator Edward J. Markey, Democrat of Massachusetts and a veteran of the health care fight, said about the precision, persistence and luck that would be required to pull off the legislative two-step. “It happens, but it happens rarely.”

Angering Republicans and unnerving more moderate Democrats, Ms. Pelosi has insisted the House will take up the popular public works bill only when it can also pass a separate, still developing measure packed with Democratic safety net priorities, including expanding Medicare and offering paid family and medical leave. That stance puts pressure on Democrats who avidly support the infrastructure legislation to also get behind the $3.5 trillion expansion of government programs outlined in the budget the Senate approved early Wednesday.

It also gives Democratic leaders some flexibility in addressing progressive Democratic complaints about shortcomings in the infrastructure bill, which was negotiated by centrists. They can try to add more climate change provisions and other elements seen to be lacking in the bipartisan bill to the budget measure that is protected from a Republican filibuster.

If House Democrats leave untouched the infrastructure bill the Senate passed Tuesday, they can approve it and send it to the president’s desk as is. In 2010, Ms. Pelosi engineered a similar approach to the Affordable Care Act, accepting unchanged the health care bill that passed the Senate with 60 votes before the seat of Senator Edward M. Kennedy, who died a year earlier, was unexpectedly taken by a Republican, Scott Brown.

She answered House grumbling about the Senate bill’s inadequacies with a follow-on, filibuster-proof budget bill that made tweaks to the health law and no longer needed 60 votes.

The prospect that Democrats could get both the infrastructure deal and their bigger package on health and social issues infuriates conservative Republicans. They complain that Democrats are having it both ways, claiming bipartisanship on the public works bill, then going full partisan to get the rest of what they want on the budget bill.

“The American people are so confused by the Democrats’ sleight of hand that they don’t even notice that their wallet has been stolen,” said Senator Bill Hagerty, Republican of Tennessee, who stalled a final vote on the infrastructure deal because of his objections. “There can’t be a bipartisan deal on infrastructure if its enactment into law requires tacking on all of the socialist wish-list items that got excluded from the deal.”

Though they did not plan the approach 11 years ago, Democrats found themselves in need of similar procedural gymnastics after Mr. Kennedy’s death. He was temporarily succeeded by Paul Kirk, a longtime Kennedy ally, who maintained the 60-seat Democratic majority that passed the Senate version of the Affordable Care Act in an extraordinary vote on Christmas Eve in 2009.

Then, a few weeks later in January 2010, Mr. Brown won a stunning upset in the special election to replace Mr. Kennedy, depriving Democrats of their filibuster-proof majority and any chance to pass a final health care bill that was to be negotiated with their counterparts in the House.

Democrats began a frantic search for a way to enact the top domestic priority of President Barack Obama. After a final fruitless attempt to find common ground with Republicans during a high-profile February summit at Blair House, across the street from the White House, Democrats decided they had no choice but to go it alone.

Democratic leaders decided the House would approve the basic Senate bill — an enormous blow to the pride of House Democrats, who had worked for months on their own version of near-universal health insurance — and send it to Mr. Obama. Along with it would come a budget reconciliation bill that made numerous changes to satisfy Democratic critics. They tossed in other domestic policy priorities, including a major expansion of federal student lending.

“Once Brown took over, we didn’t have the votes,” Max Baucus, a former Democratic senator from Montana who was chairman of the Finance Committee at the time, said about the loss of the Massachusetts seat. “So we just shoehorned it in with reconciliation.”

To make sure the Senate would deliver, the House delayed action until the Democratic leader Harry Reid guaranteed he had the necessary votes to pass the fixes to the bill. The House then approved both the health care bill and the budget measure on March 21, 2010, a Sunday. The Senate followed with its own approval of the budget bill the next Thursday, with Mr. Biden, then the vice president, presiding over the Senate to handle procedural fights and be on hand for the conclusion of a tortuous process.

“The bill as amended is passed,” said Mr. Biden, employing a bit of low-key Senate vernacular at the climatic moment.

Circumstances today are vastly different, and the budget bill taking shape is much more sweeping. Democratic leaders have linked the two measures as “hard” infrastructure and “soft” infrastructure, but Democratic moderates — and many Republicans — see the bills as distinct ventures.

The drafting of the social policy bill under the protection of budget rules is likely to touch off numerous Democratic clashes over cost and scope. Complicating the effort is the fact that Democrats have much thinner majorities now and will not be able to afford defections. In 2010, three Democratic senators abandoned the budget bill in the end and almost three dozen House Democrats bolted. If Senate Democrats today lose a single vote, the effort will die.

Senators Joe Manchin III of West Virginia and Kyrsten Sinema of Arizona, both Democrats, have both sounded the alarm about the cost of the Democratic budget plan though they joined the rest of their Democratic colleagues early Wednesday to begin drafting the legislation.

In the House, Ms. Pelosi also has far less room to maneuver than she did in 2010. She already faces a push-and-pull between progressives demanding maximum spending and more aggressive policy from the reconciliation bill and centrists anxious about the spending level who would prefer that Democrats take the bird in the hand and pass the infrastructure bill as quickly as possible. House moderates indicated on Wednesday that, at least for now, Ms. Pelosi did not have the votes to pass the Senate’s budget blueprint.

The need to hold on to every Democratic vote ultimately gives all lawmakers leverage to make demands as they did in 2010 when some anti-abortion Democrats nearly derailed the health care bill before reaching an accommodation with Ms. Pelosi and ultimately backing it. No doubt today’s bill will be in dire straits and then rescued repeatedly.

As for Republicans, they will do all they can to frustrate the Democratic effort and promote Democratic discord.

Enacting policy through reconciliation has other pitfalls as well; the Senate’s complicated budget rules enable supporters to go only so far. The Affordable Care Act suffered for years from deficiencies that could have been avoided had it been enacted in the traditional way and smoothed out as it made its way through the process.

But Democrats see no alternative to the path they are headed down and are hoping to repeat the success of 2010.

“I am very pleased to report that the two-track strategy is right on track,” Senator Chuck Schumer, Democrat of New York and the majority leader, said Wednesday as he celebrated the twin legislative victories on infrastructure and the budget.

Keeping it there will be very difficult.