How do we know? Well, he's somehow convinced everyone that Ted Cruz is a reasonable and worthy choice for president. With those kinds of powers I'm sure Trump will be able to bend China to his will just by talking tough.
Of course the latest "unpresidential" thing Trump said is that women who get abortions should be punished. Republicans were shocked. Shocked! Then they went back to saying that abortion is murder and that doctors performing abortions are killers and should punished accordingly. I never understood why women were left out of that chain of logic. If anything, the doctor is only the accomplice. At any rate, Trump's comment was a classic gaffe, meaning he inadvertently told the impolitic truth.