President Donald Trump has a social-media site. He says market-moving things on that site, which is now selling early access to those things for $100,000 a month. But the investors I’ve talked to this week who are willing to admit they might sign up see a different kind of value. They’ll be less likely to overreact and better able to distinguish the TACO stands from messages with longer-lasting market effects. It’s the oldest money-making trick on Wall Street, updated for a president whose mouth writes checks his policy apparatus can’t cash.