Yeah, it was in 1912. TR returned to the GOP fold and endorsed Charles Evans Hughes in 1916, saying that Wilson had been a disaster and he must be defeated. (Similar to Pat Buchanan, Bob Barr, etc., crawling back to the GOP after their previous third party runs screwed the GOP)
I would argue Wilson was the most left-wing of the three major candidates in 1912. Perhaps his campaign rhetoric wasn't that radical (like all lefties, even today, I'm sure he claimed to be a "fiscal conservative" and said he would run government more effectively and save money), but his true agenda certainly was. For example, Wilson wanted to nationalize the railroads, whereas Teddy Roosevelt denounced the plan as "rank socialism". If TR had run to the left of Wilson, it would have been more difficult for Wilson to win because TR would have pulled away some liberal Democrat voters from him. I think the data shows Wilson' support was actually weaker than the RAT nominees in 1908 and 1904, but he won because TR and Taft split the vote of self-described "Republicans" almost evenly.
Another thing I've noticed is politics in 1912 shows just how far we've deteriorated in 100 years. Certainly there's no doubt that TR was on the left end of the GOP spectrum in 1912 and was a "progressive" by the standards of the day. But again, I would argue both parties have moved leftward since then, so many of the positions that TR had in 1912 would be considered "ultra conservative" today -- especially Teddy's stance on guns and immigration would have 2013 Democrats portray him as a "xenophobic immigrant hating NRA puppet gun nut"
No doubt that is so, but you wouldn't have known it from listening to Wilson and the DNC's lying *sses. The Progressive's official platform was certainly the worst of the 3 parties.