The wide-open field for the 2028 Republican vice presidential nomination stems from the lack of an anointed successor after the prior cycle, leaving Marco Rubio with the highest trader-implied probability due to his Senate tenure, foreign policy background, and cross-faction appeal. John Thune trails as another Senate leader with institutional ties, while scattered support for figures such as J.D. Vance, Kristi Noem, and Elise Stefanik reflects differing priorities around base mobilization, executive experience, and regional strength. Key differentiators include legislative records, primary-season visibility, and alignment on trade, immigration, and regulatory issues. Consolidation could occur through early endorsements from major donors or governors, strong midterm results, or signals from the eventual presidential frontrunner narrowing the field before formal selection.