IMO even TR's showing in OTL was deceptively large because it was boosted by sympathy generated by the attempted assassination:
"By October, the Bull Moose party showed signs of following the traditional route of American third parties, of proving less potent in November than in August. Three weeks before the election, however, the party received a figurative and almost literal shot in the arm, when a would-be assassin wounded its candidate during a Milwaukee speech. Roosevelt, with his unfailing sense of the dramatic, finished the speech before going off for a two-week stay in the hospital. In an election already decided, his gallantry doubtless reaped a large sympathy vote. 'This shooting will help TR directly by stopping his talking,' assessed Brandeis. 'There seemed to be very strong evidence of an ebbing tide before.' In a probably exaggerated estimate, one Democrat suggesting that the assailant, 'instead of murdering the intrepid Teddy...shot about a million votes into him.'" David Sarasohn, The Party of Reform: Democrats in the Progressive Era, p. 148
The only thing I can see is some terrible last-minute scandal involving Wilson or whoever is the Democratic nominee.