President Donald Trump was gravitating toward endorsing Texas GOP Sen. John Cornyn last week. But he and some top advisers grew frustrated after his intentions leaked to the press, sources familiar with the matter told CNN, and the plan stalled. Then Cornyn’s opponent, Texas Attorney General Ken Paxton, announced on Friday that if the Senate passed the president’s voting restrictions bill — something Trump has grown particularly fixated on in recent weeks — he would consider dropping out of the runoff race. Paxton specified the GOP should lift the filibuster to do so, an idea many Republican senators oppose. White...