The president should confound expectations, pivot, and turn to the Democrats for a bipartisan deal.

Here is the tradition. If you are Franklin Roosevelt in 1935 and you want to create Social Security—an act that affects Americans very personally—you get the other party in on it. You need them co-owning it, invested in it. You want the American people saying, “Congress did this,” not “the Democrats did this,” because if they say the latter the reform will always divide. FDR got 81 Republicans to vote for it in the House, and 284 Democrats. The same with Medicare in 1965: Lyndon Johnson did all he could to get the GOP on board. A majority of House Republicans supported it.

Barack Obama, full of himself after his 2008 victory and surrounded by triumphalist House Democrats, ignored the teaching of history and passed ObamaCare without a single Republican vote. The Democrats would get all the credit. In time they got all the blame. Republicans had no incentive to bail them out.

But the health-care system, as Ohio Gov. John Kasich has observed, is crucial. The Democrats must be in on the process to achieve “true and lasting reform.”

No doubt Democrats would clean up the program along more liberal lines than Republicans, which would please their progressive base. But it would also please many in Mr. Trump’s base.