Two questions:
How was Trump polling just 3 months ago?
And two, when is the first primary/caucus?
http://www.nytimes.com/interactive/2016/us/elections/primary-calendar-and-results.html?_r=0
Trump trailed by 2 in IA to Walker back on July 26, and trailed Bush by the Mason-Dixon FL poll 28-11, but just the day before in the PPP FL poll he was up 19-17 over Walker with Bush at 12.
Go here for poll histories. I'm sure I missed one or two, but the overall trend has been steadily upward for Trump, not just nationally, but in every single state poll except WI (I think). There, Walker leads big.
http://www.realclearpolitics.com/epolls/2016/president/us/2016_republican_presidential_nomination-3823.html