* It’s October 11th. Election day is less than four weeks away. Yet the Tribune’s pollster is still surveying registered voters? That’s not great…

With national surveys showing the contest between Democrat Barack Obama and Republican Mitt Romney tightening, a new Tribune/WGN-TV poll shows the home-state president retains a comfortable advantage in Illinois even though the economy has drained some of the enthusiasm.

Obama scored 55 percent support to 36 percent for Romney, virtually identical to a similar poll in February before Romney had clinched the nomination.

This poll isn’t worth a whole lot unless you factor in the fact that registered voters tend to lean more Democratic than likely voters.

So, with that in mind, here’s a real problem for the Democrats…

…Obama’s slipping support among white suburban women. The voting group, which is considered politically moderate, favored Obama 63 percent to 30 percent eight months ago. Now Obama’s backing has fallen to 50 percent, with 43 percent backing Romney.

That’s not good news for Democrats. White suburban women are the key to statewide races.

* Not that Obama is gonna lose Illinois, but his performance will impact down-ballot candidates. For instance…

The poll asked a generic congressional support question. In Chicago and suburban Cook County, large majorities of voters said they would vote for an unspecified Democratic candidate for Congress. Even in the Republican-rich collar counties, 48 percent of voters said they’d side with a Democrat compared with 41 percent for a GOP contender.

That dynamic could help Democrats in three suburban contests: the northwest and west suburban 8th District, where Democrat Tammy Duckworth is challenging freshman Republican Rep. Joe Walsh, the north suburban 10th District where Democrat Brad Schneider is pitted against freshman GOP Rep. Robert Dold, and the far west and southwest suburban 11th District, where former Democratic Rep. Bill Foster is running against veteran Republican Rep. Judy Biggert. Chicago TV is full of millions of dollars in attack ads as interest groups try to sway voters.

But there also are three hard-fought congressional contests Downstate. Outside the Chicago region, 48 percent of voters said they’d side with a generic Republican, compared with 42 percent who preferred a Democrat. That lay of the land could help Republicans retain two seats and pick up a third now held by a retiring Democrat.

Again, adjust those Democratic numbers down and you can see the problem here.