A runoff election is a follow-up election required when no candidate in an initial contest meets a legally mandated vote threshold — typically 50% plus one vote. Texas requires a runoff when no primary candidate clears the majority threshold. Runoff electorates tend to be smaller, more partisan, and more ideologically intense than general election or even initial primary electorates, which can dramatically amplify the influence of motivated factions. In the 2026 Texas Republican Senate primary, John Cornyn (43%) and Ken Paxton (41%) both fell short of 50% in the March 3 primary, triggering a May 26 runoff. Trump endorsed Paxton on May 19, seven days before the runoff, in an environment where the compressed timeline and low-turnout dynamics maximized the impact of a presidential signal to the activist base.