The first event is the IA caucus on Feb. 1, same day as the NH primary.
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
Without even checking, I know that Trump was polling at between 1 and 3% just 3 months ago(that is around 1st of June), and was far far behind Walker who was leading all the national polls. The Iowa Caucus is not for another over 5 months to go. You can't assume that today's poll numbers for Ted Cruz or anyone else will be the same come Jenuary. Trump's own poll trajectory should tell you that. What we do know is that Ted Cruz has a solid organisation in all the states that count, strong grass roots support as confirmed by the fact that he has raised more from more people than anyone else on the Republican side(175,000 people contributed in the last quarter alone). He has the organisation and the money to fight for as long as it takes.