But the fear among liberals is that if the bipartisan measure gathers enough momentum to quickly pass, some Democrats — particularly centrists like Senators Joe Manchin III of West Virginia and Kyrsten Sinema of Arizona — will lose their appetite for another major economic package, or will force progressives to substantially scale back the scope and cost of any such plan before they are willing to vote for it. Progressives in the House warn that their support for the infrastructure agreement is contingent on the success of the bigger bill, which could amount to several trillion dollars and which Democrats plan to push through using a budget maneuver known as reconciliation to shield it from a Republican filibuster. “The president can say he’s bipartisan, he can go out and support the deal, but at the end of the day, if he wants it, he’s going to have to support our priorities,” said Representative Pramila Jayapal, Democrat of Washington and the chairwoman of the Progressive Caucus, which represents 93 House members.