Flipping the seat being vacated by Congressman Aaron Schock from Republican to Democrat will be difficult. Though the boundaries of Illinois' 18th congressional district have been redrawn several times, it has been solidly Republican for decades, with no Democrat garnering more than 41 percent of the vote in its past 10 congressional races. That doesn't lead U.S. Sen. Dick Durbin (D-Ill.) to be too optimistic about the chances of turning the district blue.

That district is a challenging district for Democrats. Not impossible, but very challenging, Durbin said. When the map was drawn, it was a Republican district. I can't tell you who is going to run or who is likely to win, but it leans Republican.

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It's Illinois'second-most Republican district, with a Cook Partisan Voting Index score of R+11. No Democrats have yet announced their intention to run, though on the Republican side, State Sen. Darin LaHood (R-Dunlap) has confirmed his candidacy for the seat held by his father, Ray, from 1995 to 2009.

State Sen. Bill Brady (R-Bloomington), who declined to run in the special election, is confident the district won't elect a Democrat.

I don't think so, but you've always got to run campaigns with concern, Brady said. I believe that the values of this district are better represented by the Republican Party, and the voters will choose that.