One thing to keep in mind is that Minnesota was competitive in 2000 and 2004. Bush lost it by 2.5 points in 2000 and 3.5 points in 2004. It's not as much of a red state as most think.
Like Oregon, Minnesota only looks competitive in 2000 because of a dramatic Nader factor. One reason Nader did well there was because it
wasn't seen as very competitive through much of 2000, allowing Minnesotan liberals to consider casting a protest vote, and then Nader decided to campaign there further. Eventually Gore had to start campaigning there, too, which was one of the first occasions that Democrats started getting really pissed off at Greens for screwing with the campaign dynamic.