President Trump has proudly stretched the power of the presidency in never-before-witnessed ways. But it's the choices he's made with that power — often alone, often impulsive — that explain his plunging popularity and will define his second term. Why it matters: Every president tests limits. Trump tests them faster than anyone, often with little thought about the consequences, his advisers tell us. Only courts or markets, or his quest for good press, can rein him in. By then, the tariffs are