One such district, the Illinois 13th, stretches from Collinsville in the west and south up through central Illinois and includes Springfield, as well as Bloomington and Champaign-Urbana.

The incumbent is Republican U.S. Representative Rodney Davis, a 44-year-old from Taylorville. The 2014 election marks Davis' first time defending his seat.

After years of serving as a congressional aide and a couple of previous failed bids for lower offices, he was selected at the 2012 Illinois Republican Convention to be the party's nominee for the race in the 13th district. He was chosen when the previous incumbent, Tim Johnson, retired after that year's primary.

Davis' road to re-election faces two stops: the March 18 primary against former Miss America winner Erika Harold and the presumptive Democratic candidate, former judge Ann Callis, in the general election.

Harold announced her campaign last summer and provoked immediate backlash from her own party. In one notorious incident, a county GOP chief, who later resigned over his comments, referred to Harold as a "street walker" working for the Democratic Party.

In a more restrained assessment, another Republican county chairperson said the issue was not that Harold was running, but only that she had challenged an uncontroversial incumbent:

"She could have selected any other office (with a Democratic incumbent) and she would have had everyone behind her. . . . We always prefer that we don't have (in-party) candidates run against our incumbents unless they've done a bad job. And Rodney Davis has by no means done a bad job."

Despite some fundraising troubles, and holding together a campaign staff, she has acquired endorsements from former presidential candidate Herman Cain and Family-PAC chairman Paul Caprio. Davis has safely secured the support of the party establishment.

raised over $500,000. A true swing district, Callis has been cautious about whether she would accept support from Governor Pat Quinn and President Barack Obama -- leaders in her party. In 2012, Mitt Romney won the district with 48.9 percent to Obama's 48.6 percent.

In her statement announcing her candidacy, Callis said she is "frustrated" Washington is not "delivering for the middle class." Illinois' unemployment rate of 8.6 percent is still higher than the national average of almost 7 percent.

Davis is considered one of 2014's more vulnerable incumbents. National Journal and Roll Call have both identified the 13th district as one that could flip this year.

Davis won in 2012 by only about one thousand votes out of more than 294,000 votes cast. An independent candidate also received over 7 percent. The three-way race meant Davis won the election on less than 47 percent of the vote and will likely need to spend 2014 proving that he has a mandate and deserves another term.