Donald Trump really only has one vulnerability, and that is his ego. Oh, some will say he is mostly concerned about his worth, but that is really just a metric for ego. Same with his women. His wives and other reported conquests are just a way of measuring his ego.
This also applies to politics. His ego makes him feel like he always has to ‘win’ an interaction, and his main way of doing that is to make sure he gets the last word in. That is why, after a relatively benign meeting with German Chancellor Angela Merkel, he felt the need to tweet something out afterwards that pretty much insulted her.
The same thing with the FBI testimony on wiretapping the Trump Tower. He could not let the FBI have the last word, so he tweeted with his comments during the testimony.
Trump’s opponents may have figured out that he has this massive ego, but they have no idea what to do with it. They just think, “His ego has got to get the better of him at some point, right?”. Unfortunately for them, they are wrong. He rides his ego like a surfer rides a wave.
The only way to exploit his Achilles Heel is to get him on a wave that is too big for him to ride safely. Like in the movies, when a character is dared into a situation beyond their control. Get under his skin and he may wipe out spectacularly.
Trump likes Twitter? Engage him in a Twitter war. Yes it is undignified, which has scared off all of the ‘proper’ politicians, even someone like Al Franken who should match up well.
There is one person who does not seem to mind using Twitter and who also seems to be very successful at getting under Trump’s skin: The Governator, Arnold Schwarzenegger. He has been out of politics for a few years, but it looks like he can’t resist a challenge either.