When former President Barack Obama said he was “heartened” by anti-Trump protests, he was sending a message of approval to his troops. Troops? Yes, Obama has an army of agitators — numbering more than 30,000 — who will fight his Republican successor at every turn of his historic presidency. And Obama will command them from a bunker less than two miles from the White House. In what’s shaping up to be a highly unusual post-presidency, Obama isn’t just staying behind in Washington. He’s working behind the scenes to set up what will effectively be a shadow government to not only...