He’s done it before, and he’s doing it again.

Donald Trump arrives for Regis Philbin’s farewell episode of “Live! with Regis and Kelly,” in New York, Nov. 18, 2011. (AP Photo/Charles Sykes)

In his new book, “Time to Get Tough,” Donald Trump lashes into President Barack Obama and threatens to run against him next year if the Republicans don’t nominate a strong candidate. Beating the drum even louder, Mr. Trump details his net worth—which he puts at $7 billion—and says he’s prepared to pour a large chunk of his $270 million in liquid assets into a presidential bid. (Mr. Trump values the Trump brand alone at $3 billion.) “He’s prepared to finance an independent run for president if he’s not satisfied with the Republican nominee,” says the real estate mogul’s right-hand man, Michael Cohen. Mr. Trump made noises about a presidential campaign this spring, including a high-profile, campaign-style jaunt aboard his personal jet to New Hampshire. But he decided instead to stick to his business enterprises and his reality TV show…