KYIV, Ukraine — Ukraine woke Wednesday to a glaring display of the potentially expanding range — and possible limits — of American support.

Hours after former President Donald Trump refused to say whether he wanted the U.S. ally to win the war against Russia, Kyiv welcomed Washington’s top diplomat — hoping he will bring a long-awaited shift on its use of long-range weapons.

Secretary of State Antony Blinken’s visit offered a show of support at a critical moment in the conflict while…