By now, it’s obvious to everyone with open eyes that Donald Trump is an ignorant, wildly dishonest, erratic, immature, bullying egomaniac. On the other hand, he’s a terrible person. But despite some high-profile defections, most senior figures in the Republican Party — very much including Paul Ryan, the speaker of the House, and Mitch McConnell, the Senate majority leader — are still supporting him, threats of violence and all. Why?

One answer is that these were never men and women of principle. I know that many in the news media are still determined to portray Mr. Ryan, in particular, as an honest man serious about policy, but his actual policy proposals have always been transparent con jobs.

Another answer is that in an era of intense partisanship, the greatest risk facing many Republican politicians isn’t that of losing in the general election, it’s that of losing to an extremist primary challenger. This makes them afraid to cross Mr. Trump, whose ugliness channels the true feelings of the party’s base.

But there’s a third answer, which can be summarized in one number: 34.

What’s that? It’s the Congressional Budget Office’s estimate of the average federal tax rate for the top 1 percent in 2013, the latest year available. And it’s up from just 28.2 in 2008, because President Obama allowed the high-end Bush tax cuts to expire and imposed new taxes to pay for a dramatic expansion of health coverage under the Affordable Care Act. Taxes on the really, really rich have gone up even more.