Donald Trump is the first president in U.S. history to have been baited into undermining his own negotiating position by negative TV coverage.Less than 12 hours after Attorney General Jeff Sessions explained that the administration is ending DACA because it’s unconstitutional, Trump tweeted that he might “revisit” the program if Congress doesn’t act.This was an implicit admission that he’s bluffing on DACA, which gives Democrats every incentive not to trade anything meaningful for a codification of the program.