Rep. Robert Dold (R-Ill.) has raised more than half a million dollars since the beginning of April in preparation for what will likely be a tough reelection campaign. Dold has reported $748,000 cash on hand for the race.

The freshman congressman's suburban Chicago district, which already leaned strongly Democratic at the presidential level, became even more liberal due to a redrawing of the map in a process controlled by state Democrats. The old district gave President Obama 61 percent of its vote; the new one would have given him 63 percent.

Dold narrowly won the district by a 51 percent to 49 percent margin in 2010, a great year for Republicans; this was one of seats Dems had hoped to pick up last year. With home-state favorite son Obama on the top of the ticket next year, it will be harder for him to hold the seat.

The district is also an expensive one because it is in the Chicago media market. Dold and his opponent combined spent almost $6 million in the last election.

The crowded Democratic field to challenge Dold includes businessman Brad Schneider, who has more than $300,000 cash on hand, and liberal activist Ilya Sheyman, who has the backing of Howard Dean, his old boss at Democracy for America. State Rep. Carol Sente is also considering a run.

Dold is just one of several Illinois Republicans facing a tough election year due to gerrymandering. Illinois Democrats passed a redistricting map that could end the House careers of six Republicans. Others in trouble because of the new map include Reps. Judy Biggert, Joe Walsh, Adam Kinzinger, Timothy Johnson and Randy Hultgren.

The map will be challenged in court.