“Pelosi and Schumer have enormously difficult jobs — they really do — and it’s easy to disparage them, to criticize them, but they have no margins with which to deal with,” Mr. Sanders said in an interview. “It’s not a job that I envy, a job that I could do for three minutes.”

Mr. Sanders has decided the best way to make the case for his vision is through outreach to Republican voters, including in-person conversations in Republican-leaning districts in Indiana and Iowa. Having relished his past interactions with voters on the campaign trail, he was back in his element, far from the staid corridors of Capitol Hill.

“This is way outside of what normal budget committees do, but on the other hand, I feel very fortunate to be in this position at this moment,” Mr. Sanders said, drinking iced tea on the patio of Midtown Station, a restaurant near the fire station, after his question-and-answer session. “In fact, if I weren’t so preoccupied with the reconciliation package and having to deal with members of Congress, etc., etc., I would probably take the Budget Committee on the road all over this country.”

“That’s what we should be doing,” he added. “We’ve got to explain to the American people what we’re doing here for them, and it can’t simply be an inside-the-Beltway process.”

But whether in Washington or in Iowa, Mr. Sanders has little patience for discussing the procedural details of the reconciliation package, focusing instead on the policy ideas he jots down in sprawling cursive. In opening remarks at a nearby park before a crowd of hundreds fanned out in lawn chairs and on picnic blankets, Mr. Sanders offered a brief warning that Senate rules could “put you to sleep in about three seconds.”

“It’s complicated, it’s boring, etc.,” he told them.

Yet those mind-numbing details will be crucial. The need for Democrats to be virtually unanimous in their support will drive the process, determining which policies can be included and which will have to be jettisoned. And the Senate parliamentarian, as the arbiter of the chamber’s rules, will potentially advise dropping certain provisions because they do not directly affect taxes and spending, a requirement for items included in reconciliation bills.

Glossing over those specifics, Mr. Sanders reassured the crowd — largely a gathering of his acolytes from across the state — that his vision would become law despite the opposition of people like Mr. Manchin and Ms. Sinema.