CHICAGO (CBS) — Veteran U.S. Sen. Richard Lugar (R-Ind) is facing the biggest challenge of his long career, trailing in the polls heading into Tuesday’s primary.

Lugar, 80. is bidding for his sixth term, but is behind his primary opponent, Indiana State Treasurer Richard Mourdock.

WBBM Newsradio’s Dave Marsett reports, Tea Party members have been working to topple Lugar after 36 years in the Senate. The winner of Tuesday’s primary will face Democratic U.S. Rep. Joe Donnelly in November.

Lugar supporters offered various reasons for Lugar’s difficulties. Miami County prosecutor, Bruce Embrey, says Lugar’s supporters got caught off guard. Peru Mayor Jim Walker blames the Tea Party, who he says believe “compromise” is a dirty word.

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