LONDON — Boris Johnson issued a direct plea to Donald Trump not to ditch U.S. support for Ukraine if he becomes president in 2024.

Writing for the Spectator after a trip to Ukraine, the former British prime minister — who has lobbied hard for wavering Republicans to keep the faith in the war-torn country — warned Russian triumph could boomerang on any Trump administration.

“A Putin victory would be a catastrophe for the West and for American leadership, and I don’t believe it is an outcome that could easily be endured by a U.S. president, let alone one who wanted to Make America Great Again,” Johnson wrote in the Spectator.

Johnson said that should Ukraine succeed in repelling Russia, “then the reverse is true.”

“Exactly the opposite message will be sent around the world: that we do care about democracy, that we are willing to back our principles, and that the West still has the guts to stick at something until we succeed,” he added.

Johnson’s comments come amid Ukrainian jitters about what a Trump presidency would mean for Western support.

Since being forced from office last year, the ex-British leader has energetically lobbied for continued support for Ukraine. In May he attended a private lunch in Dallas, Texas, as part of efforts to shore up support for the Ukrainian war effort with skeptical Republicans. And he dined with Trump on the same trip, with a Johnson spokesperson saying he stressed “the vital importance of Ukrainian victory.”