In the past three days, Republican leaders in the Senate scrambled to corral votes for a tax bill that the Joint Committee on Taxation said would add $1 trillion to the deficit — without holding any meaningful committee hearings. Worse, Republican leaders have been blunt about their motivation: to deliver on their promises to wealthy donors, and down the road, to use the leverage of huge deficits to cut and privatize Medicare and Social Security.

Congress no longer works the way it’s supposed to. But we’ve said that before.

Eleven years ago, we published a book called “The Broken Branch,” which we subtitled “How Congress Is Failing America and How to Get It Back on Track.” Embedded in that subtitle were two assumptions: first, that Congress as an institution — which is to say, both parties, equally — is at fault; and second, that the solution is readily at hand. In 2017, the Republicans’ scandalous tax bill is only the latest proof that both assumptions are wrong.

Which is not to say that we were totally off base in 2006. We stand by our assessment of the political scene at the time. What is astounding, and still largely unappreciated, is the unexpected and rapid nature of the decline in American national politics, and how one-sided its cause. If in 2006 one could cast aspersions on both parties, over the past decade it has become clear that it is the Republican Party — as an institution, as a movement, as a collection of politicians — that has done unique, extensive and possibly irreparable damage to the American political system.

Even today, many people like to imagine that the damage has all been President Trump’s doing — that he took the Republican Party hostage. But the problem goes much deeper.