They're not going to, so don't worry. If the GOP couldn't really make any inroads to these states in the last 10 years, they probably won't. In fact, I think the Democrats' strength in MN, WI and MI has gotten that much stronger in the past few years. IA is a bit more hazy.
Dems have gotten better organized in MN, but they've done quite poorly in WI- ever heard of the Scott Walker recall?
Of course, that's on the state level, where party organization (and gerrymandering) matters. Michigan is actually to the left of Minnesota (though not by much) but the DFL and MI GOP are both extremely strong state parties which are able to successfully win and get their agenda passed.
