Mr. Trump’s political instincts haven’t helped him with conservatives. He decides day-to-day what to say and frequently speaks off the cuff. He is often rash and undisciplined. His conservative detractors, especially those in policy and media circles, are appalled.

To bring stability to his campaign, Mr. Trump now plans a series of formal speeches on policy issues, set pieces drafted by speechwriters and delivered from prepared texts. This assumes Mr. Trump follows through with the speeches. Avoiding distractions may result from the recent hiring of a professional campaign manager, Paul Manafort.

The model is his speech last month in Washington, D.C., to the American Israel Public Affairs Committee (Aipac). He used the address to correct the impression he had left in a televised debate that he would not be a strong defender of Israel. Speaking to Aipac in a sports arena, he read the text on a Teleprompter with few ad libs. He got several standing ovations.

In a similar way, Mr. Trump wants to use the policy speeches to persuade conservatives, among other skeptics, that he is more in sync with their thinking than they imagine. If he fails, Republican defectors or a third-party conservative candidate would doom his already slim chance of winning the presidency.