SAN DIEGO — In Don Winslow’s crime novels, characters regularly face dangers they should have seen coming. Those who ignore the warning signs often wind up dead. Now in the middle of a 23-city, nationwide tour promoting his newest book, the Julian-area writer said he is worried about a different kind of looming danger: threats to American democracy. He’s so worried that he’s retiring from writing books. He said he’ll devote his energies full time to the political activism he started engaging in about six years ago via Twitter posts, short films and newspaper ads. “I’m not a huge name, but I ha…