Previous Trump promises, threats and cajoling have failed to yield results., and the stubborn diplomatic stalemate will be hard to clear away. Meanwhile, Ukraine is losing more territory on the front line, although there is no sign of a looming collapse of its defenses.

President Trump has given an ultimatum to President Vladimir V. Putin of Russia to end the war in Ukraine or face U.S. sanctions.

President Trump on Monday lambasted the “Russian war machine” responsible for the deaths of innocent Ukrainians — in a sharp escalation of his rhetoric just as special