Topeka — Republican U.S. Sen. Pat Roberts sought Wednesday to undercut an independent candidate’s appeal to unaffiliated Kansas voters by declaring that the challenger is a liberal Democrat and pointing to past campaign contributions.

But the independent challenger, Greg Orman, a 44-year-old Olathe businessman, dismissed the 78-year-old, three-term incumbent’s criticism as an “old, tired attack.” He also noted that he’s given far more money to centrist causes, such as the Common Sense Coalition, a nonprofit group he helped form to promote “the sensible center.”

“The criticism from both sides doesn’t surprise me,” Orman said. “We live in a world where most of our politicians only think in terms of red or blue, so everybody has got to be a shade of red or blue.”

Meanwhile, Democratic nominee Chad Taylor, 40, the Shawnee County district attorney, challenged Roberts to debate him in each of the state’s 105 counties — which would require the candidates to have more than one event a day. Roberts said he’s launching a 105-county listening tour of the state next week.

“Chad is the reasonable, moderate alternative,” campaign manager Brandon Naylor said.

Roberts spoke during a brief GOP rally at the state party’s Topeka headquarters, calling for Republican unity. Afterward, reporters asked Roberts whether a serious independent candidate complicated his re-election.

The senator said: “But he’s not an independent. He’s another liberal Democrat.”

Orman ran for the U.S. Senate in 2007 as a Democrat, intending to challenge Roberts as he sought a third term, but he dropped out early in 2008.

Online campaign finance records show that Orman contributed more than $40,000 to other candidates or party organizations since 2006. The list is bipartisan but leans Democratic, with contributions to Democratic presidential candidates Barack Obama and Hillary Clinton in 2007 and to the Kansas Democratic Party in 2009.

But Orman’s campaign released a document showing that he’s contributed more than $288,000 to the Common Sense Coalition since the start of 2009, and said his total contributions to centrist groups totals more than $300,000. Orman said giving to both parties and having them disappoint him led him to conclude that he had to challenge the two-party system.