The White House plan for a massive package of tax cuts is gaining new momentum as Republicans attempt to set aside months of intraparty squabbling and unify behind a key part of President Trump’s agenda.

Two developments are accelerating the effort: Key Senate Republicans reached a tentative deal this week to allow for as much as $1.5 trillion in tax reductions over 10 years; and there is a growing willingness within the GOP to embrace controversial, optimistic estimates of how much economic growth their tax plan would create.

Those upbeat estimates, often rejected by nonpartisan economists, would supplant the traditional forecasts offered by official scorekeepers at the Congressional Budget Office and Joint Committee on Taxation, helping lawmakers argue that the plan would not increase the national debt.

Trump is pushing for what he says will be the largest tax cut in U.S. history, which advisers say will come from a sharp decrease in corporate tax rates and tax relief for the middle class.