If the modern Republican Party can be said to stand for anything, it is tax relief. Yet as the Republican effort to write and pass tax legislation develops, it looks increasingly possible — and perhaps even likely — that it, like the health care overhaul attempt that preceded it, will end in failure and disappointment.

When the year began, the speaker of the House, Paul Ryan, cited health care and taxes as his top legislative priorities, predicting that both would be completed by August. Yet after nine months of party control of Congress and the White House, the Republicans have accomplished essentially nothing. They have become a party without a consensus.

It would be easy to simply blame the president for the party’s disarray. Donald Trump’s aversion to policy detail, his chaotic management style and his combustible personality have all contributed to the party’s failures this year.

Yet it would also be a mistake to pin the party’s problems on Mr. Trump alone. He is not their root cause. Instead, he is an avatar of the party’s pathologies, the culmination of its cynical and shambolic trajectory over the last two decades.