Trump on Tuesday endorsed Texas Attorney General Ken Paxton in his primary challenge to Sen. John Cornyn, dealing a massive blow to the incumbent with major implications in the fight for the Senate majority. Cornyn has spent over a year courting Trump's support, while Paxton has run to Cornyn's right and pitched himself as a stronger ally of the president. Cornyn and Senate GOP leaders argued that he is a stronger general-election candidate as Democrats look to win statewide office in Texas for the first time since 1994. The runoff is a week away, and early voting began Monday.