When President Donald Trump fired a broadside at NATO allies in Brussels on Wednesday, complaining once again that other nations are not paying their fair share for the alliance’s defense and labeling Germany a “captive of Russia,” he was displaying the same hyperaggressive negotiation style that has defined not only his first 500 days in office but his nearly 50-year business career.

In just the past month, he belittled Canadian Prime Minister Justin Trudeau as “weak” and “dishonest” and vowed to levy taxes “like never before” on iconic U.S. manufacturer Harley-Davidson after learning it might move some manufacturing overseas. He has even mocked members of his own party whom he considered insufficiently loyal, costing him key votes on major legislation.

But this high-volume, public shaming strategy—while winning headlines that play well with his political supporters—hasn’t delivered the negotiating results he has promised.

I have been studying and teaching negotiation for 25 years and, over the past 18 months, have studied over 100 of Trump’s business deals over the course of his almost five decades of negotiating, examining them for evidence of the traits used by history’s most celebrated negotiators. I’ve concluded that the man who made his career promoting himself as the ultimate deal-maker is far less effective than he thinks and often doesn’t negotiate well based on the experts’ proven research.