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.

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.