President Donald Trump’s endorsement remains a dominant factor in Republican primaries, particularly in the closely watched Texas U.S. Senate runoff between incumbent Sen. John Cornyn and Texas Attorney General Ken Paxton scheduled for May 26. Trump has repeatedly delayed a decision despite promising one “relatively soon” after the March 3 primary, citing positive views of both candidates while facing pressure from MAGA-aligned groups over Cornyn’s recent reposting of content critical of the president and stalled Senate action on the SAVE America Act. Early voting begins May 18, intensifying the timeline. Trump’s recent endorsements in other 2026 contests, including successful challenges to dissident Republicans in Indiana, have reinforced his influence on voter turnout and primary outcomes, leaving traders focused on whether he will back an incumbent or a challenger in this high-stakes race.