Vice President Kamala Harris’ trip to Warsaw to thank Poland for taking in hundreds of thousands of Ukrainians fleeing Russia’s invasion took an unexpected turn before she even left Washington. She’ll be parachuting into the middle of unexpected diplomatic turbulence over fighter jets. The Polish government on Tuesday came out with a plan to transfer its Russian-made fighter planes to a U.S. military base in Germany, with the expectation that the planes would then be handed over to Ukrainian pilots trying to fend off Russian forces. In turn, the U.S. would supply Poland with U.S.-made jets with “corresponding capabilities.” But...