(CBS) – Republican Jim Oberweis is his party’s candidate to try to unseat longtime incumbent U.S. Sen. Dick Durbin in the November election.

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Oberweis, an entrepreneur, dairy owner and state senator from Sugar Grove, was considered a lock to wrest the GOP nomination from Downers Grove businessman Doug Truax, though the race was tighter than expected Tuesday.

Addressing his supporters in the western suburbs, Oberweis wasted no time in tearing into Durbin. He described the Democrat as a career politician who has spent 32 years in Washington helping drive up the national debt.

The Republican called Durbin “a guy who has compared our military to the Nazis” – a reference to a controversial 2005 comment Durbin made about the treatment of military detainees, for which he later apologized.

Oberweis had 56 percent of the vote (240,661 ballots cast for him), to Truax’s 44 percent, with 63 percent of precincts counted.

Jim Oberweis addresses supporters Tuesday after winning the GOP nomination for U.S. Senate. (Chris Martinez/CBS)

Jim Oberweis addresses supporters Tuesday after winning the GOP nomination for U.S. Senate. (Chris Martinez/CBS)

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Truax, in his concession speech, said it had been a “tough race, a tough campaign” but urged his supporters to back Oberweis to defeat the incumbent.

Durbin, attending Gov. Pat Quinn’s election-night gathering in Chicago, said he would not take anything for granted leading up to the general election.

“Anyone who takes an election result for granted is going to lose,” he told CBS 2’s Dana Kozlov. “I won’t let myself ever get in that position.”

The senator, who ran unopposed Tuesday, said he’ll emphasize to voters his experience in Washington and his connections to the White House.

A political stumble last week called Oberweis’ frontrunner status in the primary into question.

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He drew unwanted attention by traveling to Florida during the home stretch. Oberweis said he took his wife to Florida for her birthday after having made mistakes in his first marriage. Truax said the secretive trip came across as arrogant.