O'BRIEN: Trump believed Ukraine had no cards, that he could bully Ukrainians into giving Putin very good deal.
He didn't understand that Ukraine was developing their own capabilities and their willingness to fight.
So, Trump failed for two reasons. First, Ukrainians adapted, and that wasn't expected by him.
You can see there have been some changes in his rhetoric lately, where he has to grudgingly admit that Ukraine has actually done better.
The United States completely underestimated Ukrainian resilience.
Secondly, Trump thought Europeans would bully Ukraine along with him because they would be afraid of United States leaving NATO.
He thought he could use NATO to push Europeans to force Ukraine to take a bad deal. Europeans eventually helped Ukraine more than he thought.
They seem to understand that it's actually better for them to have Ukraine fight the war the way Ukraine wants.
Trump didn't understand what Ukraine was capable of and he misjudged what Europeans would do.