For President Vladimir V. Putin of Russia, it is an opportunity not just to end the Ukraine war on his terms, but to split apart the Western security alliance.

None of that matters to President Donald Trump, who announced Friday night that he would meet the globally shunned leader this Friday in Alaska. What does matter to Trump is that he may be able to stop the bloodshed in Ukraine, the worst European conflict since World War II, fulfilling one of his biggest campaign promises.

The threats, pressure and ultimatums have come and gone, but Russian President Vladimir Putin has maintained Moscow’s uncompromising demands in Ukraine, raising fears he could use a planned summit with U.