@PolAmKrakow
While we can't know for certain what Trump would have done, I would argue that your scenario does not align with Trumps' actual policies and his later statements.
We know that Trump
- was dismissive of Ukraine and tried to blackmail it to provide it with dirt on Biden in exchange for military aid
- wanted to leave NATO, let the Europeans handle things and generally avoid getting dragged into new conflict
- had great sympathy for strongmen like Putin
- was easily manipulated by them due to his vanity and habded them great successes on the diplomatic stage (e.g North Korea or his various meetings with Putin).
Not to mention what he has said since then about his hypthetical actions.
Based on all of that it seems pretty clear what what would have happened if Trump had been in charge:
-The USA would have left NATO
-Putin would have called him and after some flattery Trump would have told him that the Europeans were on their own and did not deserve American help
- Emboldended by this Putin would have invaded
- Trump would not have dreamed of offering significant aid to Ukraine when he was already complaining about "freeloading" Europeans. It was not an American problem and the Europeans were reaping the results of their actions. The same man who made a great deal of his planned withdrawel from Afghanistan would hardly have been willing to step up elsewhere.