It is one of the most closely watched races in the nation, and it is one of the keys to determining control of the U.S. Senate.

Incumbent U.S. Sen. Mark Kirk is trailing Democratic U.S. Rep. Tammy Duckworth by 14 points in the most recent pollconducted by the Paul Simon Public Policy Institute at Southern Illinois University.

Kirk insists that news of his political death is premature. However, Duckworth also leads in the fundraising race, hauling in three times more campaign cash in the last quarter with $4 million on hand to his $1.4 million.

Duckworth has A-listers campaigning for her in Chicago including President Barack Obama and David Letterman. She also received Hillary Clinton’s endorsement in September.

Kirk is a moderate Republican who supports gun control and gay rights.

Duckworth nabbed Chicago’s two major newspaper endorsements made by the Chicago Tribune and the Chicago Sun-Times. The Daily Herald endorsed Mark Kirk.

So what separates the two candidates? And what do they need to do in the last two weeks of the campaign to convince the roughly 10 percent of undecided voters to support them?

Duckworth joins host Carol Marin for a one-on-one discussion. Kirk declined our invitation, first made in July, to appear.

Both Duckworth and Kirk did not participate inChicago Tonight's Candidate Free Timebut the Libertarian candidateKenton McMillenand Green Party candidateScott Summersdid so voters can learn more about their positions.

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