In yesterday’s NYT, a piece by Patrick Healy, “For 2016 Run, Scott Walker Washes ‘Wiscahnsin’ Out of His Mouth”, beginning:
Columbia, S.C. — Out on the presidential campaign trail, Gov. Scott Walker has left “Wiscahnsin” back home in Wisconsin. He now wants to strengthen the economy, not the “ecahnahmy.” And while he once had the “ahnor” of meeting fellow Republicans, he told one group here this week that he simply enjoyed “talkin’ with y’all.”
The classic Upper Midwest accent — nasal and full of flat a’s — is one of several Walker trademarks to have fallen away this month after an intense period of strategizing and coaching designed to help Mr. Walker capitalize on his popularity in early polls and show that he is not some provincial politician out of his depth.
Although Healy leads with pronunciation matters, they are not the focus of the piece, which is about how Walker is being coached in general on ways to make himself attractive to a wide range of voters.
Now on the main dialect feature in question, the Upper Midwest “flat a”.