So far Trump’s promises, threats and cajoling have failed to shift the Kremlin’s position, and the stubborn diplomatic stalemate remains in place. Meanwhile, Ukraine is losing more territory on the front line, although there is no sign of a looming collapse of its defenses.

The coming week could bring an important moment in the war between Russia and Ukraine, as U.S. President Donald Trump’s deadline for the Kremlin to reach a peace deal approaches — or it could simply melt away.

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