The votes for the bill by Susan Collins of Maine and John McCain and Jeff Flake of Arizona were particularly disheartening. Ms. Collins, who helped sink an effort to effectively repeal the A.C.A. in September, blithely voted for a tax bill that will leave a gaping hole in that law by repealing its requirement that most people have insurance or pay a penalty. She traded away her vote for an inadequate deduction for property taxes and empty promises from Mr. Trump and the majority leader, Mitch McConnell, that they would help shore up the A.C.A., which they have repeatedly tried to sabotage. Mr. McCain, who previously voted against tax cuts in the Bush era because they were heavily tilted in favor of the rich rather than the middle class, seemed unconcerned that this bill was even worse in that regard. Then there is Mr. Flake, who has spoken powerfully against Mr. Trump and who is not seeking re-election. He folded on the basis of vague assurances about protecting the Dreamers, young undocumented immigrants brought to the country as children.

Republicans offered one fantasy after another to make the case for their budget-busting tax cuts. For example, the White House has said that cutting the corporate tax to 20 percent from 35 percent will lead to a boom in investment and wages — an argument disputed by most credible economists. Almost all of those extra profits will enrich senior executives and shareholders, experts say. This week, The Times reported that despite the repeated claims of the Treasury secretary, Steven Mnuchin, his department never produced an analysis that backs up the administration’s assertion that the tax cuts would pay for themselves. It is not hard to see why. The Joint Committee on Taxation, the Urban-Brookings Tax Policy Center and other experts say that the bill would not come close to paying for itself.

For his part, Mr. Trump has repeatedly asserted with a straight face that the tax bill would hurt him. In fact, it will give him and his family a windfall. That’s because the Senate bill will provide a generous tax break for income that people earn through limited liability corporations, partnerships and other so-called pass-through businesses that do not pay taxes before passing on profits to owners. Under the Senate bill, the president will be able to claim a 23 percent deduction on profits he earns through his more than 500 pass-through businesses.

You can expect the lies to become even more brazen as Republicans seek to defend this terrible bill. But no amount of prevarication can change the fact that Congress and Mr. Trump are giving a giant gift to their donors and sticking the rest of the country with the tab.