The League of Women Voters of Kentucky has canceled its planned U.S. Senate debate between Sen. Rand Paul and his challenger Lexington Mayor Jim Gray after Paul declined an invitation to participate.

The debate was scheduled for October 30 at the University of Kentucky and was to be broadcast live on WKYT in Lexington, WLKY in Louisville, and other television stations serving the state. Other sponsors of the debate included The Lexington Herald-Leader and University of Kentucky Student Government.

"Research conducted on voter behavior and participation shows that not only does the public expect candidates to participate in voter education activities but it also found that voters are more likely to vote when they know who the candidates are and where they stand on issues," said Dr. Terry Naydan, co-president of the League of Women Voters of Kentucky. "When candidates choose not to participate, it is a loss for the voters."

Invitations for the debate were first sent to the Republican senator and his Democratic opponent shortly after the May primaries.

Paul did accept an invitation to debate Gray on KET on October 31.

During his presidential bid earlier this year, Paul complained about not be included in a January debate on the Fox Business Network for Republicans vying for the party’s nomination.

Gray is harshly critical of Paul for his aborted presidential run, saying he has failed to represent the state. However, according to Paul's campaign spokeswoman Kelsey Cooper, the senator maintained a 96 percent attendance record for Senate votes. Cooper cited Paul's efforts to curtail the federal government's surveillance powers and protect gun ownership rights.

Paul juggled dual campaigns for the White House and re-election to the Senate until early this year, when he ended his presidential bid.

Paul rode a wave of tea party support in winning his Senate seat in 2010. The libertarian-leaning Paul kept to his low tax-and-spend mantra during his first Senate term. He also championed efforts to curtail the federal government's surveillance powers, and has ventured into minority neighborhoods to advocate for criminal-justice reforms.

Kentucky Democrats have not won a U.S. Senate race since 1992.