Donald Trump likes to brag about his negotiating skills, but for a tough negotiator, he's awfully easy to manipulate. There are two types of people in Trumpland: those who are nice to Donald, and those who are not nice to Donald. If you flatter Trump, he'll treat you well. If you criticize him, he'll retaliate. "I'm a counter-puncher," he once told CNN.

So to win Trump's favor, just say something sweet about him; Vladimir Putin praised him last December, and Trump has been preening over the compliment ever since. And to deliberately draw Trump's fire, say something nasty about him; last week Elizabeth Warren called him a bully and a loser, which dragged him into a distracting and unpresidential tweetfight with someone who is not his opponent.

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