How do you know the election season is heating up? When candidates start to debate. How do you know it's heating up earlier than ever? From the fact that the first debate of the season takes place not on Labor Day, but on Bastille Day.

Democratic Rep. Mark Udall and former Republican Rep. Bob Schaffer, who are battling over retiring Senator Wayne Allard's seat, will meet today at the Wildlife Experience, a nature conservation museum about ten miles south of Denver, for the first of what promises to be a fiery series of debates.

Sponsored by 9News, Denver's NBC affiliate, the candidates will face a moderator but will have plenty of chances to interact with each other, and both will have plenty to say. Republicans cast Udall as too liberal for the state, while Democrats have criticized Schaffer for ties to Jack Abramoff and to a disputed oil deal in Iraq.

The Democratic Senatorial Campaign Committee counts Colorado as one of five states currently held by Republican Senators in which their candidate is leading. The latest public poll, taken in mid-June for Quinnipiac University, shows Udall leading by ten points, aided by a huge advantage among independents and a massive gender gap.

Adding to the pressure on Schaffer, Udall announced this morning he had pulled in more than $2 million during the Second Quarter, ending with $3.9 million in the bank. The campaign spent significantly on a statewide television campaign over the last two months, reducing the approximately two-to-one cash-on-hand advantage Udall held over Schaffer. Still, the Republican will likely continue to trail in cash in the bank when he reports his own haul by tomorrow.

The hour-long debate is only the first meeting between the two candidates. Negotiations are under way for a second debate, to take place on Denver's Fox affiliate, though details have yet to be worked out. Schaffer has proposed seven debates over the Summer alone.

To watch today's debate, click over to 9News for a live stream at 10 a.m. Mountain Time, or noon on the East Coast.