In addition to the farm crisis--which was the catalyst for the Democratic resurgence in the Midwest states, the Democrats had a much stronger presence in the Plains in the 1980s and 1990s--on a statewide level. For years, you had one or two Democratic senators in Nebraska and the Dakotas, and they elected several Democratic governors as well. They were generally more conservative than the national party, but they were widely accepted within the party and held leadership positions as well.
I checked the employment stats for Iowa. and Iowa's economy slumped in 1979 and would not recover until May 1988. Which is as close to a decade as you can get. So by election day in November of 1988 a lot of people voted Dukakis as a protest vote.
http://research.stlouisfed.org/fred2/series/IANANIronically that farm crisis started as a result of the US banning agricultural exports to the USSR, an action undertaken by Carter. A lot of the great plains states and one even like North Dakota that Carter had lost by 6% in 1976 was lost by 38% in 1980.
http://research.stlouisfed.org/fred2/series/B181RC1Q027SBEAAgricultural exports peaked in 1981 and would halve by 1987 and would not recover until 1994. And boomed afterwards.
