Garssley should have another fairly routine election in 2016. That being said, the Democratic party would love to draft Secretary of Agriculture and former Governor Tom Vilsak. Though they have another former Governor they wouldn't mind drafting in Chet Culver. The only polling has been from last fall from PPP and only in regards to Vilsak. Their last poll last fall to include the 2016 Senate race gives Grassley a 51%-42% lead. That gives Grassley a decent cushion to start with. While Iowa is a light blue seat, Grassley has had a long hold on this seat and will likely continue to have in 2016.
Grassley could still face a primary challenge to the right. Representative Steve King would be the most probable challenge but his jumping in is not quite likely. He, after all, declined to run in 2014 for Harkin's open seat. If he were to run and pull off the upset against Grassley, this seat would become very much in play. That being said, don't count on any of that happening.
IA-1: This is the seat that will be the most competitive in 2016. This is a seat that was heald by 2014 Senate candidate Bruce Braley and narrowly won, in a very good GOP year, by Republican Rod Blum. Even a 2014 rematch could likely flip this seat back to blue.
President: This is a state where Hillary Clinton would be highly favored to win in 2016. Both PPP and Gravis give Clinton various leads over all GOP candidates. In this blue leaning state, Clinton would end up winning that state almost definitely so long as she wins nationally. That being said, it would be a single digit victory against most potential GOP rivals.