I believe Iowa and North Carolina are both good targets for us, but I see Iowa as more winnable, even though North Carolina will be more competitive in the Presidential Race, simply because we have a larger bench in Iowa to choose from.
More candidates does not mean more good candidates. If Trump wins Iowa by double digits, there's no way Joni Ernst loses barring a breathtaking scandal. Also, Ernst is much more popular than Tillis and will almost certainly run ahead of Trump. Tillis may very well run behind Trump.
I doubt Trump will win IA by double digits this time (though he'll probably still win it).