I’m the underdog,” David McCormick told NewsNation’s Leland Vittert in a one-on-one interview for “On Balance.”

With about one month before the election, incumbent Democratic Sen. Bob Casey faces GOP businessman Dave McCormick Thursday in their first debate.

Pennsylvania Sen. Bob Casey (D) is up 4 points in his Senate reelection bid over Republican rival David McCormick, according to a new survey. The AARP poll found the incumbent Democrat garnering 49 percent support from likely voters to McCormick’s 45 percent,

Pennsylvania's Democratic Sen. Bob Casey and Republican Dave McCormick speak with NBC News' Julie Tsirkin about why they differ from each other and how they are striking a balance with the top of the ticket.

Casey, perhaps Pennsylvania’s best-known politician, is seeking a fourth term and is facing what he calls his toughest reelection challenge yet. Casey, 64, is a staunch ally of labor unions, a former state auditor general and treasurer and Pennsylvania’s longest-serving Democrat in the Senate.

With about one month before the election, incumbent Democratic Sen. Bob Casey faces GOP businessman Dave McCormick Thursday in their first debate.