Cristie is number 3 in NH, but at the bottom in Iowa. He is making much more of an effort in NH, so it makes sense he is polling better in NH.
There have been millions of dollars of ads purchased in Iowa. In Virginia, I have seen zero ads. The candidates are all over Iowa, but not in Virginia - so yes, I would expect a national poll and an Iowa poll to be different.
It’s not that Iowa and the national polls are different, it’s that this poll and the poll showing Cruz up by 10 were so far different than other similar polls from the same timeframe. Sometimes polls are just outliers. Sometimes there are sampling issues. Other times, some polls catch a trend quicker than others.
In a few days, we will be able to see which it is in this case.