For President Donald Trump, a peace agreement to end the war in Ukraine is his ultimate diplomatic white whale — an elusive goal on which he staked his reputation as a nonpareil deal-maker. And which, if accomplished, just might secure the Nobel Peace Prize he believes he’s been denied. 

It was a year ago, at a U.S. military base in Alaska, that Trump thought he could hammer out a deal with Russian President Vladimir Putin, whom he considered a friend.