Trump was indeed volatile, impulsive, and capricious. It’s certainly possible that Putin feared a move against Ukraine could spark a massive military response from Trump.

But it’s far more likely he hoped for something very different. As Jonathan Last pointedly suggested on Tuesday in his newsletter for The Bulwark, Trump expressed his desire on numerous occasions for the United States to withdraw from NATO altogether. He did so while campaigning for president in 2016. He did so as president. And apparently, he even made clear to advisers he hoped to make it a reality after he won re-election in 2020.

Since such a withdrawal is Putin’s fondest wish, it makes far greater sense to suppose his relative restraint during the Trump presidency was a function of a reasonable expectation he might get everything he wanted without having to fire a shot. Only now, with a less … unorthodox American president in charge, has war become Putin’s only means of advancing his more immediate aim of ensuring NATO moves no closer to Russian territory.