Recent Republican midterm losses tied to the ongoing Iran conflict and President Trump’s low approval ratings have driven JD Vance’s 2028 GOP nomination odds down from near 50 percent earlier this fall to roughly 31-34 percent on major prediction markets. Traders view further erosion as likely by December 31 amid reports that Vance is weighing whether to run at all, with allies noting the environment may not favor any administration-linked candidate. Rivals including Marco Rubio and Ron DeSantis have gained ground while positioning for the primary, and any visible progress or setbacks in ending the Iran war before year-end could quickly shift implied probabilities in the short resolution window.