Donald Trump, the best golfer ever to set up shop in the Oval Office, announced in London this week that because of departing Prime Minister Theresa May’s efforts, the Brexit deal is “teed up.” Teed up? With this remark, Mr. Trump gives new meaning to “mulligan,” golf’s infamous do-over for a failed shot. Britain’s politicians are at least 40 shots over par on Brexit, having shanked, hooked or topped every ball they’ve tried to hit.

In truth, there’s nothing funny about the British elites’ hapless efforts to make good on...