Let's say that Wilson does a little worse in the election, only getting about 36% of the popular vote, with most of his support going to Roosevelt, but a little to Taft. The vote loss is concentrated in non-southern states. However, his slightly weaker performance allows several close states to go to Roosevelt or Taft. Roosvelt and Taft also manage to win their home states of New York and Ohio.
These states are:
California (virtual tie OTL, the 2 electoral votes that went for Wilson go for Roosevelt)
Idaho (1% margin of victory, 4 electoral votes to Taft)
Illinois (2% margin OTL, 29 electoral votes to Roosevelt)
Iowa (5% margin OTL, 13 electoral votes to Roosevelt)
Kansas (6% margin OTL, 10 electoral votes to Roosevelt)
Maine (2% margin OTL, 6 electoral votes to Roosevelt)
Massachusetts (3% margin OTL, 18 electoral votes to Taft)
Montana (7% margin OTL, 4 electoral votes to Roosevelt)
New Hampshire (2% margin OTL, 4 electoral votes to Taft)
New Mexico (6% margin OTL, 3 electoral votes to Taft)
New York (15% margin OTL, Roosevelt's homestate, 45 electoral votes to Roosevelt)
North Dakota (4% margin OTL, 5 electoral votes to Roosevelt)
Ohio (14% margin OTL, Taft's homestate, 24 electoral votes for Taft)
Oregon (7% margin OTL, 5 electoral votes to Roosevelt)
Rhode Island (3% margin OTL, 5 electoral votes to Taft)
Wisconsin (9% margin OTL, 13 electoral votes to Taft)
Wyoming (2% margin OTL, 3 electoral votes to Taft)
The electoral college ends up 242 votes for Wilson, 207 for Roosevelt, and 82 for Taft. The popular vote is approximately 36% for Wilson, 31% for Roosevelt, and 25% for Taft.
Will Taft or Roosevelt's electors go to Wilson, perhaps with some deal between the candidates? Will the three sides refuse to cooperate, and the election go to the Democrat-controlled House that will probably vote in Wilson? Or will the Taft Republicans decide to join with Roosevelt instead, giving him the election? Or perhaps even unification of 2 of the sides around some new compromise candidate?