Glenn Thrush of Politico has a column on Yahoo News that points to some potentially worrisome signs for Obama heading into the conventions. Of Michigan he writes:

Michigan’s in play for McCain. In the year of the downturn, the hard-hit upper Midwest should be prime Obama country. Instead it’s a potential minefield. Obama is still ahead by two to five points there — similar to margins of victory enjoyed by Gore and Kerry in the last two presidential contests — but McCain has quietly crept up over the past month and could vault ahead if he anoints ex-Gov. Mitt Romney as his running mate. Simmering tensions between predominantly black Detroit and its white suburbs could hurt Obama. And McCain’s surrogates were handed a gift in the jailing of Detroit Mayor Kwame Kilpatrick, an Obama supporter.

“Watch Michigan — the Democrats think they’ve got it but they don’t,” says Quinnipiac’s Peter Brown, a longtime Michigan observer. “Obama should be killing [McCain] there, but there’s a lot more racial tension in Michigan than in other states.”

Obama also hasn’t pulled away in other Democrat-friendly neighboring states, watching leads in Wisconsin and Minnesota erode over the last month.

I don’t think McCain has a serious shot at winning Wisconsin or Minnesota, despite some tightening of the polls in those states in recent weeks. Wisconsin is a strong blue state and Obama still leads the polls by an average of 8 points. Minnesota is also strongly Democratic in presidential elections — it’s the only state Reagan didn’t carry in the 1984 election, for crying out loud — and the Quinnipiac poll that showed Obama with only a 2-point lead appears to be an outlier. The three other most recent polls, including another by Quinnipiac, showed him with a lead of 13, 17 and 17 points, respectively. Take away the one anachronistic result and the lead is much larger.

But I agree with Thrush and Brown on Michigan. This is a swing state, but Obama should have a much larger lead. Polls from June 10 to July 10 showed Obama with an average lead of 7 points; polls from July 11 to now show an average lead of only 3.2 points, with no poll showing more than a 4-point lead. That is within the general margin of error of such polls, making Michigan a toss-up state at this point. I think ultimately Obama still wins Michigan, but it is by no means a given. Obama is going to have to work hard in this state, despite McCain’s blunders here (praising a Central American free trade agreement in Detroit, for example).