President Obama has issued 145 “midnight” regulations with a cost of more than $21 billion since the election of Donald Trump, the most by a lame-duck president in a generation, a study has found. The conservative American Action Forum said Thursday that Mr. Obama’s rules, issued from Nov. 8 through Dec. 31 of last year, include 31 “economically significant” regulations with a cost of at least $100 million each.