This is a drop of 6 points from Cruz and a rise of 1 point for Trump since the same polling company survey December 7-10.
The Quinnipiac, ARG and PPP polls taken at the same time have Trump ahead of Cruz by 31% to 29% 20% to 25% and 28% to 26% respectively.
The four major polls average out at Trump 27.50% and Cruz 26.25%. Clearly there is nothing between them at this point poll wise but just as clearly the momentum which saw Carson decline and Cruz take a substantial lead in December, is all with Trump. The challenge to Cruz of Trump's hitting hard on Cruz's eligibility to be president, having been born in Canada and having had Canadian citizenship is surely not yet fully picked up by these polls and may further increase Trump's lead at this vital point.
The "ground game" i.e. getting supporters to the actual caucus may negate any polls and momentum for wither or any candidate but for the moment the tide has turned in Trump's favor.
In the Huffington Post "Poll of Polls" aggregate Trump's momentum line has overtaken Cruz
Adding to the Trump momentum story new Gravis OANN poll has Trump moving ahead 34% to 28%