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.

Suppose I want to buy a used car from you. Normally, we would start by agreeing about the basic facts: number of miles, dents, etc. I’d run a CarFax report to see if it had been in any accidents. Then we would argue about what the car was worth.

But what if I showed up and even though the CarFax report was clean, I said that I believed that the car had been in an accident.

“Huh? The CarFax report is clean,” you would respond.

“Well, I have heard of plenty of times where you cannot trust CarFax. And I am sure this car has been in an accident.”

At that point you would normally tell me to get lost. But if you had to sell I were the only buyer around you would find yourself fruitlessly arguing with me and trying to prove a negative – that the car had not been in an accident. I would just keep repeating the lie that it had, no matter what evidence you produced to the contrary.

Eventually, I would figure that I had worn you down enough and start my ‘real’ negotiation. Most of the time I would get a better deal than if I started out agreeing with you on the basic facts.

There aren’t a lot of people who use lying as a negotiating tactic because it tends to piss people off so much that they won’t do business with them. But if I am the head of a very large company and brand, or the president of the United States, people have no choice but to do business with me and there is really not a lot of downside to using the technique.

Everyone knows the old adage that “you cannot prove a negative.” Can anyone prove that there haven’t been space aliens in the custody of the US government? No, because there really is nothing anyone can do to offer up satisfactory proof that it never happened.

Donald Trump is a master of the “negative proof accusation”. Ted Cruz’s family had something to do with Kennedy’s assassination? How can Cruz prove that this is not true. It is impossible. The same for many of Trump’s other accusations during the campaign.

Once he because president, the tables turned when he was accused of collaborating with the Russians to win the election. How can he prove this is not so? Worse for him, several of his trusted advisors were proven to have interacted with the Russians during the campaign (i.e., they admitted it) making it look more likely that it happened.

What does Trump do? What he has always done when he gets in a hot spot. He changes the subject, goes on the attack and accuses Barak Obama of a no-no. And of course, Obama cannot prove that he did not do it, because as Trump knows, you cannot prove a negative.

The problem for Trump is proving a positive. That can be done. And if people start proving things against him that hurt, he might not be able to keep coming up with negative accusations to deflect the bad news. Actually, that is incorrect. He will always be able to come up with these, the issue is whether anyone will listen anymore.

He has one more card up his sleeve though. When Trump gets caught doing something that he ostensibly shouldn’t, he turns the tables and claims that what he is doing is actually very crafty and smart. When he finally admitted that he was not paying taxes he immediately claimed that it was a smart move.

If his collaboration with the Russians is proven, my guess is that Trump will retort that:

• We (the US) always do it (meddle in elections) – why shouldn’t the Russians?
• The Russians are not getting any special favors – look at how disappointed they are in some of our policies
• It was smart – I took advantage of the Russians’ help to win and now I am not giving them anything back

His supporters will probably accept this. The question is whether the Republicans in Congress buy in as well.