How worried is the Obama campaign about Minnesota, one of the bluest of blue states?

This worried: they’re sending Bill Clinton there for a visit tomorrow.  Clinton is taking his show around the country to states where Obama’s firewall is collapsing: Minnesota, Iowa, Colorado, Virginia, New Hampshire, Wisconsin and Ohio.

A Star Tribune Minnesota Poll, published Sunday, shows that Obama’s lead has plummeted to the point where there is only a three-point differential between Obama and Mitt Romney, which is within the poll’s margin of error.

Both campaigns have stepped up their advertising in Minnesota, and Romney or Paul Ryan may stop there this week.

Minnesota has voted for the Democratic presidential nominee every election since 1972, but in 2000 and 2004 the margin was slim. In 2000, Gore only got 59,000 more votes out of 2.5 million that were cast, while in 2004, Kerry got 99,000 more votes out of more than 3.1 million cast. Gore won the state 48% to 45.5%, and Kerry won 51% to 47.6%.

But the key is this: in a Star Tribune poll last month, Obama had an eight-point lead, and now it has dwindled to three. Romney is closing fast.