The Republican National Convention has done a remarkably thorough job so far in making a case against presumptive Democratic presidential nominee Hillary Clinton. What more can be done after one prime-time speaker leads the crowd in chants of “guilty” (with “lock her up” spontaneously interspersed by the delegates) and another posits just two degrees of separation between her and Lucifer? What America needs to hear when the GOP nominee takes the stage tonight — remarkable though it may be to say this about someone so famously prone to self-promotion — is the case for Donald J. Trump.

In nominating the New York businessman, the Republican Party has done an extraordinary thing. Mr. Trump is the first major party candidate in the history of the nation with no previous public service in either government or the military. Just three people have ever been elected president without having previously won elective office, and they were all war heroes: Dwight D. Eisenhower in 1952, Ulysses S. Grant in 1868 and Zachary Taylor in 1848. Mr. Trump has no record in office to serve as a guide to the public in evaluating how he would perform as president, and he has displayed a penchant for self-contradiction on policy matters that would make Walt Whitman blush. (To paraphrase “Leaves of Grass”: “Do I contradict myself? Very well, then I contradict myself, I am huuuuuge, I am worth billions, and we will win.”)

Mr. Trump gave a preview of his convention address to Fox News host Bill O'Reilly on Monday night, promising a “pretty large speech in terms of what it's going to cover.” He mentioned law and order (“We have to demonstrate from our politicians, who are pretty weak now, law and order”), border security (“We'll be talking about the wall”), the “tremendous tax decrease we're going to be given,” cutting regulations, boosting the military, taking care of veterans, the Affordable Care Act and more.

We certainly don't expect a wonky policy speech — that's neither Mr. Trump's style nor the type of address that suits the occasion — but we do hope he will go into more than his usual level of detail. It's one thing to say, as he did to Mr. O'Reilly on Monday for example, “We're going to get rid of Obamacare and come up with a plan that is so much better, so much less expensive,” but another to give some idea of what that might be and how it would affect the millions who have gotten coverage under the ACA. It's one thing to say he would negotiate better trade deals but another to sketch out a vision for how America competes in a globalized economy. Certainly, let's get rid of ISIS, but what does that mean about when and how we will send troops overseas?

What the voters need tonight is a cohesive picture of what the country would look like under a Trump presidency. We have heard a lot of fear and anger from the convention so far but not much vision. House Speaker Paul Ryan did a good job in his remarks Tuesday night sketching out his own ideas about the future, but there was precious little trace in them of Donald Trump. If the nominee is looking for a model to follow, he could do worse than the speech by his son, Donald Trump Jr., on Tuesday night. The younger Mr. Trump was poised, polished and focused in a way that his father typically isn't, in an address that spanned personal, political and policy issues with equal fluency.

During the primaries, Mr. Trump generated tremendous enthusiasm from many voters who were disaffected by politics and finally felt someone was speaking to them. During the Republican convention so far, he has made progress in unifying the GOP. Tonight is his chance to speak to the rest of America, including many voters who are terrified at the prospect that he will win in November. This week, his supporters have contended that Democrats are the ones who divide America and that Mr. Trump will unite them. This speech is his chance to prove it.