Shortly after Democrats rallied behind Kamala Harris as the party’s 2024 nominee, Donald Trump thought the smart move would be to launch a series of personal attacks. A great many Republicans offered some simple advice: Stop.

Sen. Lindsey Graham appeared on NBC News’ “Meet the Press” in August, for example, and issued a public plea. “President Trump can win this election. His policies are good for America, and if you have a policy debate for president, he wins,” the South Carolina Republican said. “Donald Trump the provocateur, the showman, may not win this election.”

Trump, of course, ignored the advice for a variety of reasons.

For one thing, the former president has said he feels “entitled“ to launch personal attacks. For another, Trump, at least on some level, likely knows that his policies aren’t especially popular.

But there’s long been a problem that his party struggles to fully appreciate: Trump doesn’t talk about policy because he can’t. The former president has never been able to speak coherently about governing, and with three weeks remaining before Election Day, nothing has changed.

The Atlantic’s David Graham summarized the Republican’s appearance at the Economic Club of Chicago this way: “When Donald Trump speaks about the economy, he sounds like a child.”

China gives us billions of dollars via tariffs. American auto workers take imported cars out of a box and stick the pieces together. These are very light paraphrases of statements he made today at the Economic Club of Chicago, in a sometimes combative interview with the Bloomberg editor in chief John Micklethwait.

At times, it was difficult to watch. Asked, for example, about the dramatic impact his plans would have on the national debt, Trump said a great many words, none of which answered the question. Asked about Google — a company the former president has threatened to prosecute in response to a conspiracy theory he concocted — the GOP candidate changed the subject.

Trump didn’t seem to know what the chairman of the Federal Reserve does. He spoke a great deal about trade tariffs but struggled with the details. He talked about reserve currencies but didn’t seem to know what they are. When the conversation turned to small businesses, the former president talked about Apple — prompting his host to explain that Apple is not a small business.

At one point, Trump thought it’d be a good idea to insult auto industry workers, claiming that children could do their jobs just as well. Around the same time, in response to a question about cutting federal spending, he shared an anecdote about Air Force One that wasn’t true.

In June, the Business Roundtable offered the Republican an opportunity to meet privately with a room full of leading CEOs. One told NBC News after the discussion, “Trump doesn’t know what he’s talking about.”

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He still doesn’t.

It’s not as if Trump occasionally has bad days but is otherwise up to speed on economic policy. The night before the event in Chicago, a voter asked him about addressing the price of groceries, and his long, meandering answer was effectively gibberish.

Two days earlier, the GOP candidate effectively admitted that when it comes to proposed trade tariffs, he essentially just makes up numbers off the top of his head. “Until now I’ve said 200[%],” he told Fox News. “I’m using that just as a figure. I’ll say 100, 200, I’ll say 500, I don’t care.”

For months, Trump has been repeatedly asked how he intends to address inflation, and he’s never been able to answer in a coherent way.

I can appreciate why Republican officials keep urging their nominee to focus on policy, but they’re effectively asking squirrels to do trigonometry: If Trump could talk about the substantive details of governing and policymaking, he would. But he can’t, so he doesn’t.