On Sunday, Donald Trump acknowledged that his deportation operation had been too tough. By Thursday, he was threatening to double tariffs on Mexico over a northbound migrant caravan. His moderation has the shelf life of an avocado left on a radiator.

Reuters reports that about 1,500 people, mostly Central Americans, left Tapachula near Guatemala on Tuesday. They hope the incoming Democratic Congress might create a path to live and work in the United States. Hope is not a visa. Nor is a congressional election a switch that opens the border in January. But apparently people walking in southern Mexico are enough to put the trade relationship on the president’s emotional-support trampoline.

Why negotiate one difficult issue when you can tie it to another and yank?

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Mexican president Claudia Sheinbaum says no caravans have reached the US border since Trump returned to office. She says Mexico is explaining the difficulty of entry, seeking to return people to their home countries and rejecting repression. That is her account, not a promise that every migration problem has been solved.

Trump’s tariff increase is a threat, not an implemented change. The two governments are already negotiating trade. Imagine being the negotiator who thought today’s difficult question would concern trade, and discovering that your entire assignment is now attached to the president’s caps-lock key.

The migrants aren’t the joke. Powerful people turning their uncertain journey into a remote control for an unrelated negotiation are.

Sunday’s Trump was open to an immigration deal with Democrats. Thursday’s Trump demanded no leniency. If the two could meet, perhaps Mexico could get a quiet afternoon.