Overland Park ? U.S. Sen. Pat Roberts hoped Kansas’ deep Republican roots would hold firm Tuesday as he sought to fend off a surprisingly staunch challenge from a suburban Kansas City businessman pledging to bring a nonpartisan voice to Washington.

Should Greg Orman defeat the three-term senator in one of the nation’s most unusual and potentially pivotal races, he would become Kansas’ first independent in the U.S. Senate. In fact, the state hasn’t elected anyone but Republicans to the office since 1932.

Roberts, 78, has served in the Senate for 18 years — after spending 16 years in the U.S. House — and is seeking another six-year extension by highlighting his party affiliation. He says his re-election is essential to Republican efforts to wrest control of the chamber from Democrats and provide a legislative check on the policies of President Barack Obama.

Orman, 45, has cited Roberts’ loyalty to Republicans as an example of a broken political system that he says has ground Washington to a halt. Orman, who also has criticized Democrats, has campaigned by emphasizing his business expertise. He has pledged to bridge political divides but has declined to say whether he would caucus with either Democrats or Republicans if elected.

A steady stream of voters were showing up at polling places early Tuesday, including some who expressed unhappiness with the choice of candidates in the Senate race.

Ron Buck, a 44-year-old independent from Fairway who is a self-employed roofing contractor, cast his ballot for Roberts without much enthusiasm.

“They both seem kind of like leftovers you don’t want to eat, but he just seems a little bit better,” Buck said. “I’m not crazy about either of them. I wouldn’t give either of them money.”

Tom Eli, 64, a Cessna aircraft worker in Wichita, also voted for Roberts with hesitation.

“I don’t trust Orman,” Eli said. “I don’t like Roberts either. But that is the way we vote in this country. We don’t have good choices.”

Orman became the main alternative to Roberts after Democratic nominee Chad Taylor dropped out in September, a move that was viewed as a way to consolidate the anti-Roberts vote. Libertarian Randall Batson also will be on the Senate ballot.

Dean and Janice Loreg, a married couple from Topeka, are registered Republicans but said many of their views are more in line with the Democrats’ since the rise of the tea party within the GOP. They voted for Orman, although Janice Loreg said she would have voted for Taylor if he was on the ballot.

They both agreed that Roberts has been in the Senate too long.

“I just think it’s time for a change,” said Dean Loreg, a retired railroad executive. “Pat Roberts has been there a long time and I can’t think of one thing he’s done for Kansas.”

Sharon Miklos, 51, a massage therapist from Peck, voted for Roberts, partly as a vote against President Barack Obama.

“Out of the two, he is the better choice,” Miklos said. “I don’t want to give Obama any more power.”

A Marine veteran and former House Agriculture Committee chairman, Roberts never has gotten less than 60 percent of the vote in his three previous Senate campaigns. But he got just 48 percent of the vote this August while surviving a four-way GOP primary.

The first signs that Roberts faced an unusually tough re-election appeared as a tea party-backed Republican candidate, Milton Wolf, questioned whether Roberts had grown out of touch with Kansas residents during his long tenure in Washington. Among other things, Wolf noted that Roberts owns a home in suburban Washington but lists a rented room in the Dodge City home of one of his supporters as his official Kansas residence.

During the general election campaign, Roberts has tried to portray Orman as a liberal Democrat running under the guise of an independent. Orman ran briefly as a Democrat against Roberts in 2007 before dropping out of that race. Orman contributed to the 2008 Democratic presidential campaigns of Obama and Hillary Rodham Clinton, but he has also given money to Republicans, such as Scott Brown’s campaign for the U.S. Senate in Massachusetts in 2010.

Orman grew up in Minnesota where he founded an energy efficient lighting company shortly after graduating with an economics degree from Princeton University. Within a few years, he built Environmental Lighting Concepts into a multimillion-dollar business with 120 employees. Orman moved to Kansas to open a branch office of his firm and became an executive for a subsidiary of Kansas City Power & Light Co. after selling it a majority stake in Environmental Lighting Concepts in 1996.

Orman co-founded the private equity firm Denali Partners in 2004. He now lists leadership roles in 15 businesses, and his federal financial disclosure forms put his net worth between $21.5 million and $86 million. He lives in Olathe.