WASHINGTON — President Trump on Wednesday will try to sell the American people on an unpopular Republican tax overhaul that his administration claims will generate a large part of $1.8 trillion in new revenue – a figure that a top Democratic lawmaker dismissed as “fake math.”

Trump’s pitch will focus on how the Republican tax reform plan will lead to a brighter future for taxpayers and their families, said spokeswoman Lindsay Walters. House and Senate negotiators are rushing to finalize a bill and deliver the measure to Trump before Christmas.

Trump and Republican leaders in Congress have promoted the massive tax plan by promising the tax cuts will boost the economy. Their idea is that growth sparked by the legislation will let the tax cuts pay for themselves and not balloon the $20 trillion deficit.

Public polling shows many Americans are unhappy with the proposal. The House and Senate tax bills combine steep tax cuts for corporations with more modest reductions for individuals.

The administration’s rosy estimate of new revenue from the tax plan over 10 years is a lot higher than nonpartisan congressional analysts have projected. The Joint Committee on Taxation estimates that growth stimulated by the anticipated tax cuts will generate some $408 billion in additional tax revenue over 10 years.

The new Treasury Department analysis says about half the expected increase in economic growth likely will result from tax benefits for corporations. Trump and the Republicans have insisted that businesses will use the tax savings to invest and create new jobs.

According to the Treasury analysis, the other half of new revenue will come from tax reductions for individuals and businesses whose profits are reported on owners’ personal income tax returns, as well as from planned administration initiatives such as infrastructure development and a welfare overhaul.

The analysis includes an assumption that tax cuts and other administration policies would cause the economy to expand at a 2.9 percent annual pace over 10 years. Economic growth at that level would, in theory, be enough to keep the national debt from rising.

But most analyses have concluded that the tax overhaul would add at least $1 trillion to budget deficits in the next decade because the analyses foresee significantly less growth resulting from the tax cuts.

Senate Democratic Leader Chuck Schumer called the administration’s analysis “nothing more than one page of fake math.”

“It’s clear the White House and Republicans are grasping at straws to prove the unprovable and garner votes for a bill that nearly every single independent analysis has concluded will blow up the deficit and generate almost no additional economic activity to make up for it,” Schumer said.

The estimates by Treasury and the Joint Committee on Taxation apply specifically to the Senate bill. The congressional tax committee released an analysis of the House bill late Monday projecting sufficient growth to generate $483 billion in new revenue.