Ukraine has been asking for more fighters since the war started, but the US refused to support a deal that could have seen Poland supply 28 MiG-29s, a Russian-made jet of the type its remaining pilots are used to flying. Washington was concerned that supplying fighter jets could be deemed escalatory by a nuclear-armed Russia. Despite the refusals, Ukraine continues to press its case, and overnight its air force tweeted “the greatest need is for fighter jets” and asked specifically for F-15s and F-16s, whose original designs date back to the 1960s and 1970s, which it said its pilots could...