President Trump. (Kevin Lamarque/Reuters)

PRESIDENT TRUMP campaigned on a promise to build a wall between Mexico and the United States. Now, with Congress having to renew federal spending authority by week’s end, he believes he’s entitled to a down payment on that wall. What’s wrong with that logic?

A number of things, but this above all: No responsible leader would use the possible shutdown of the federal government as a political cudgel. The last time a budget impasse produced a partial shutdown, a 16-day version in 2013, some 850,000 federal employees were put through a wrenching furlough and access to national parks and the Smithsonian was curtailed, with serious consequences for tourism across the country. All told, the economy lost $24 billion, according to an analysis by Standard & Poor’s. Mr. Trump’s first priority must be to avoid repeating or doubling down on that debacle.

In a discursive interview with Julie Pace of the Associated Press, Mr. Trump suggested that the responsibility of his job indeed may be sinking in. “It’s massive,” he said of his new position. “And every agency is, like, bigger than any company. So you know, I really just see the bigness of it all, but also the responsibility. And the human responsibility. You know, the human life that’s involved in some of the decisions.”

For a man who campaigned on the notion that he possessed special capabilities that could reduce the challenges facing American government to a series of “wins,” which would occur “quickly,” as he put it, this epiphany represents progress — but only up to a point. Even as he spoke to Ms. Pace, Mr. Trump was making it more difficult for Congress to reach a deal on extending federal spending authority past its April 28 expiration date.

Specifically, he had injected a demand for an appropriation for his proposed wall along the U.S.-Mexico border, implying that, if he did not get the money, the government might have to shut. A leader truly concerned for “the human life that’s involved in some of these decisions” would not risk a repeat of the 2013 mess, especially at a time when top negotiators for his own Republican Party in Congress seemed on their way to an agreement with Democrats that would avoid it.

If he wants to make a case for his wall on its merits, and separate from budget brinkmanship, he is entitled to do so — though as we have said before, he has a weak case. It may be, as Mr. Trump told Ms. Pace, that “my base really wants it,” but the project is otherwise unpopular, including with many Republican legislators from the border region, and for good reason. A physical barrier along the entire southern border would be a colossal waste of money and a terrible symbol of American attitudes. That would be true even if, as he repeatedly promised during the campaign, Mexico would foot the bill. And it won’t.