White House run: Donald Trump poses for a portrait at Mar-a-Lago this month, the day before he announced he was running for the US presidency again. Photograph: Damon Winter/New York Times Just when you thought it was safe to go back in the water, Donald Trump is running for president again. That was not a prospect Bob Woodward had to deal with when Richard Nixon resigned in 1974, after Woodward and his Washington Post colleague Carl Bernstein cracked open the Watergate scandal. “Our long national nightmare is over,” declared Nixon’s successor, Gerald Ford, and it was. Nixon faded into jowly...