I'm not totally sure you aren't being cheeky here, but - Cave in (to someone/thing) means to stop resisting their pressure and accept their terms (while not being happy to do so)
The government caved in to the demands of the protesters. She caved in to her family and dumped her boyfriend.
Just out of curiosity, what would you support about Fico that you wouldn't about Tucker's hypothetical stance? I don't know much about him, but he seems like your average pro-Russia politician within the EU / empire, let's say.