No recent U.S. President wanted to pull out of NATO. The Clinton campaign falsely claimed that Trump did, but he just wanted other countries to pay the agreed upon 2% commitment. And it looks like it worked.
Technicalities don't mean much, Russia will make its move not based on technicalities but on the perceptions of other countries' response. Currently the front runners for the next US admin from the GOP side are openly from the "we'll give Russia anything, Putin good" camp so yes, Estonians and other Eastern Europeans are rightly concerned.
The Russians aren't gonna necessarily come across the border militarily. The Russians are gonna do what they did in Ukraine.
I'm not sure I would risk a nuclear war over some place which is the suburbs of St. Petersburg"
Unless I misunderstand, I already see the speech: "we saved millions of Americans thanks to my mastermind diplomacy, we send our prayers to all our allies, good luck!"