One thing to note that is that a lot of his support is because he is cannibalizing the support from the crowded field of candidates who are trying to court the conservative base.
http://www.realclearpolitics.com/epolls/2016/president/us/2016_republican_presidential_nomination-3823.htmlCruz, Huckabee, Carson, Santroum, Jindal. Have had 30-50% of their support flee to trump. He's gaining in the polls because he was the guy people who wanted those candidates to be. a conservative that makes a lot of noise and gets a lot of attention. Who won't backtrack or backdown.
For some reason, Carson, Cruz, Huckabee, etc were playing it safe after initial attention. Also i think some conservatives might of been turned off from the too much overt evangelical pandering by the other conservative candidates.
Strangely enough, Scott Walker is still holding on. If he can cannibalize the rest of them along with scott walker's support he could be really strong. Although time will tell whether or not he was just another flavor of the month candidate.