Colorado.
We're talking about Trump +9 with a majority vs Clinton +5 without a majority right? And in Iowa's case, the trend is greater for Republicans than Colorado is for Democrats. I don't know why that's so insane to presume.
But this all depends on what people think will happen. If most people believe 2020 is going to be some Democratic blowout (+7-10 points in the PV), then yeah, Iowa is more likely to flip.
Iowa could get much closer than it was in 16 with Trump performing similarly in the PV and even winning in the general, it wouldn't take a 2008 style blowout for Iowa to turn blue.
His near 10 point margin isn't set in stone, his trade policies affect people in agribuisness, and HRC was a poor fit for the Midwest. I say Trump wins it 3-6 points whether or not he wins the GE.
Colorado isn't going to get better for Trump than the 4.8% he lost it by in 16. The D's floor in the state is higher than the R's floor in Iowa.