“There’s gonna be some lag time,” said Senator John Kennedy of Louisiana. “How much? I don’t know. I don’t think anybody knows.” He said some of the corporate tax provisions, including a proposal to allow companies to fully and immediately deduct the cost of their equipment purchases, will have “an immediate effect” on the economy and give middle-class Americans higher take-home pay. “Yes, they’ll notice it,” he said.

“In 2018, you’ll start seeing the green shoots of some capital investment, but it’ll ramp up over about an 18 to 24 month period,” said Senator Thom Tillis of North Carolina.

Republicans in districts with lower median incomes are more optimistic about quicker effects.

‘Very Meaningful’

“It would be very meaningful to people in my district,” said Representative Bradley Byrne of Alabama. “I can tell you it’ll help me in my district. And if we don’t pass it I think it’ll hurt me.”

Complicating the picture is the fact that a minority of Americans would stand to face a greater financial burden next year -- if plans for repealing or curtailing deductions such as state and local taxes remain in place. Also, both bills repeal personal exemptions, offering a potential hit to large families.

“If you’re a husband and a wife and you have two or three kids, you bet it is significant,” said Senator Ron Wyden of Oregon, the chief tax-writing Democrat.

Republicans are hoping for the best.

“When this gets signed by President Trump, this is going to be a generational achievement,” House Majority Whip Steve Scalise of Louisiana told Fox News on Monday.

“People are going to be very enthusiastic and excited,” said Representative Karen Handel of Georgia, who won a special election in June and may face a competitive race in 2018. “They are going to be buoyed by the fact that true tax relief -- that most people haven’t seen in their entire lifetime -- they are going to be receiving.”