Democrats have no shortage of criticism for the massive Republican policy bill winding its way through Congress carrying President Trump’s agenda. It would cost too much, they contend, rip health coverage and food assistance away from too many people and strip vital support from clean energy companies.

When it comes to some of the tax cuts in the bill, however, Democrats have been less resistant. Some of them concede that they would support many of those provisions if they were not rolled into the larger piece of legislation. In recent weeks, they have taken pains to demonstrate that support.

Last month, Senator Jacky Rosen, Democrat of Nevada, successfully moved to have the Senate unanimously approve a version of Mr. Trump’s “no tax on tips” proposal. While the effort was almost entirely symbolic — under the Constitution, the House must originate tax measures — it was still an opportunity for Democrats to go on the record backing a campaign promise of Mr. Trump’s that is broadly popular with the public.

“I am not afraid to embrace a good idea, wherever it comes from,” Ms. Rosen said on the Senate floor at the time.