The Caucus doesn't work that way. You have to have multiple committed delegates in each of the 99 counties and in each of the vastly more precincts. If Trump is not highly organized and Cruz is, Cruz will still beat him even if the polls remain 25-23. You can't participate if you're an independent or a disgruntled Democrat, and Iowa has a long tradition of Caucus night where the people most interested and with political know-how have the upper hand and can turn back someone else even though they have better popular support. I would bet lots of the Trump supporters have never even been to a caucus.
2012, Romney vs. Santorum, one of them "won" the popular vote, the other won the delegates.
Its been fairly widely reported that Trump has the best ground team in Iowa. Chuck Laudner is his manager there and he got Santorum the win. That being said Cruz might have a chance in Iowa and maybe Texas. But trailing by 2-9pts is not going to do it. Close only counts in horseshoes and hand grenades.