The Texas Senate race is making Republicans nervous.Texas Attorney General Ken Paxton is challenging incumbent Senator John Cornyn in the Republican primary, and the race is so close that an expensive runoff election is possible. A runoff could draw resources away from other close elections around the country and aid Democratic efforts to flip the seat.Republican donors have poured over $60 million into the state to defeat Paxton, who is also running against Representative Wesley Hunt. But Paxto...