Two conservatives whom I like and greatly admire—Niall Ferguson and J.D. Vance—were this week involved in a social media dispute over President Donald Trump’s preliminary broadsides about the three-year Ukrainian quagmire, whose combined dead, wounded, and missing mark the worst bloodbath in Europe since the Battle of Stalingrad in 1942 and 1943.

As we approached the three-year-anniversary of the war, Ferguson faulted President Trump for calling Ukrainian president Volodymyr Zelensky a “dictator” and claiming that Ukraine had “started” the war.

In his criticism, Ferguson contrasted George H.W. Bush’s unambiguous “this will not stand” response to news of Saddam Hussein’s 1990 invasion of Kuwait. And he added that students of history will naturally ask why the current Republican president did not react in the way Bush had in faulting and then ejecting from Kuwait the clear aggressor: Saddam Hussein.

Ferguson’s observation drew a heated response from Vice President J.D. Vance. He countered that the historical parallels were ossified (e.g., Bush in 1990 was confronted with entering a war against a paper-tiger Iraq, Trump with inheriting in mediis rebus a horrific, three-year Verdun-like stalemate directly involving one of the world’s largest nuclear powers).

Margaret Thatcher wrote in her memoirs that she had to reassure Bush in a phone call after Saddam’s invasion that “this was no time to go wobbly,” and reportedly had also said the same thing to him at an Aspen conference: “Remember George, this is no time to go wobbly.”...