Senate Republicans on Tuesday vented their frustration and disappointment over President Trump’s decision to endorse state Attorney General Ken Paxton over Sen. John Cornyn (R) in the Texas Senate Republican primary, a move that deals a crushing blow to Cornyn’s hopes of winning the May 26 runoff. “I don’t understand. He is an ethically challenged individual,” Sen. Susan Collins (R-Maine) said of Paxton, who was charged with defrauding investors in a Dallas-area tech startup before he completed a pretrial diversion program. Sen. Lisa Murkowski (R-Alaska) said she was “supremely disappointed” in Trump’s endorsement of Paxton over Cornyn. “I don’t understand...