Colorado's Senate candidates are preparing for a debate Monday night in Denver.

Republican Bob Schaffer and Democrat Mark Udall both are rallying supporters for Monday's debate at Gates Concert Hall in Denver.

A few hours before the debate, Udall plans to promote endorsements from Republicans. The Udall fans include the niece of retiring Republican Sen. Wayne Allard.

Karen Allard Campbell will join Udall, who is battling Republican Bob Schaffer for the seat being vacated by Wayne Allard. Karen Allard Campbell is also the niece of former Colorado Sen. Ben Nighthorse Campbell.

Udall and Schaffer debate again Tuesday afternoon before the Denver Metro Chamber of Commerce. They have another debate planned for next Monday in Pueblo at Colorado State University-Pueblo.