On Thursday morning, The New York Times revealed that Steven Mnuchin, the Treasury secretary, has been lying for months about Republican tax plans. Mnuchin has repeatedly claimed the existence of a Treasury report that — unlike every independent, nonpartisan assessment — found that these plans would pay for themselves, increasing growth and hence revenues so much that the deficit wouldn’t rise. But there is no such report, and never has been; Treasury staffers weren’t even asked to study the issue.

Also on Thursday, John McCain — who has delivered sanctimonious lectures on the importance of “regular order” in the Senate — declared his support for the G.O.P. tax bill. Remember, Senate leaders rushed this bill to the floor without holding any hearings or soliciting expert testimony (and tax policy is an area where you really, really need to hear from experts, lawyers and accountants even more than economists). In fact, at the time McCain declared his support, some key provisions were still secret, so they could be presented for a vote with no time for debate.

McCain declared that he had made his decision after “careful consideration.” Careful consideration of what? He didn’t even wait for an analysis of the bill’s economic impact by the Joint Committee on Taxation, Congress’s own scorekeeper — the only official assessment, since the Trump administration was, as I said, lying when it claimed to have its own analysis.

Later that day the joint committee delivered its predictable verdict: Like all other reasonable studies, its review found that the Senate bill would do little for U.S. economic growth, while directly hurting tens of millions of middle-class Americans, blowing up the deficit, lavishing benefits on the wealthy and opening up new frontiers for tax avoidance. But thanks to the moral collapse of McCain and other supposedly principled Republicans, at the time this column was filed the bill nonetheless seemed on track to clear the Senate.