The most likely argument I see is that Trump severely strained diplomatic bonds both between North America and Europe and also within North America and Europe. Additionally, he heralded in a new degree of isolationist policy and created doubt about the resilience of NATO. Furthermore, he tried to blackmail the Ukrainian government.

In summary: Not his fault directly but his politics led to a situation where Russia/Putin saw it as likely that they could invade without facing significant backlash from Europe + North America. That probably would have worked out as well if Ukraine had folded within the first couple of weeks. The argument is essentially that by convincing Russia that they could get Ukraine without significant consequences, his administration contributed to the invasion happening.

Make of that argument what you will. Personally, I think it’s a bit of a stretch to say “Trumps fault”, but reasonable to think that another administration might have been able to deter the invasion.