He also attacked Tancredo's conservative credentials, specifically his decision to vote for the Troubled Asset Relief Program, or TARP, for banks, which the former congressman said was necessary at the time.
"If you're going to claim to be a conservative, you shouldn't have voted for TARP," Maes said. "And if I've proven one thing over the last 90 days is I stand up to anybody."
Tancredo, who has become a poster child for tougher immigration measures, defended his own voting record and decision to run as a third party candidate.
"I believed Dan could not win the race, and I believed John should not win the race. That was my impetus of getting in," he said today. "I didn't sneak in anywhere, I followed the law."
Experts say if immigration were as hot of a topic as it is in some border states, Tancredo could have the opportunity of a last-minute surge. But that's not the case in Colorado. Maes hasn't dropped out, as some Republicans had hoped, which has split the conservative base.
The race between Buck and Bennet is one of the most hotly contested Senate races in the country. With Colorado proving itself as a decisively purple state, Democrats are pouring millions of dollars into Bennet's campaign to cap their losses. At the same time, Republicans also see the race as an opportunity to win back a key seat in the state where independents dominate.
"There are still a reasonable number of people that are undecided, and then you have your own supporters who need to be enforced," said Democratic consultant Michael Stratton. "The strategy that candidates have right now is do no harm, kind of the hypocritical oath of politics right now."
Buck has attacked Bennet as a Washington insider closely aligned with Obama's agenda, even though the incumbent has attempted to portray himself as an independent and more of a moderate.
Bennet, in turn, has criticized his opponent for calling Social Security a "horrible policy" -- a comment that Buck later retracted -- and his comments that the Department of Education isn't necessary.
"What drives Bucks' constituencies and where he continues to hammer is that Bennet is part of the Washington establishment, votes with the president, is responsible for much of the debt we've had in the last 18 months, backed health care, which he feels is too much," said Colorado pollster Floyd Ciruli. "Bennet's going to argue that his [Buck's] plan is essentially Bush two, that it's simply what got us into this mess."
Like the rest of the country, the economy is the number one concern in Colorado. But both parties have tried to inject other issues that are important to Coloradans, like abortion and energy.
Buck has said he would sponsor a constitutional amendment to ban abortions, even in the case of rape or incest.
The Republican candidate also supported a state initiative on "personhood" that would extend legal rights to embryos and would ban any form of birth control that prevents a fertilized egg from implanting in the uterus. Most recently, he has said he won't push for such a ballot initiative, even though he supports the concept.
To help Bennet increase his female voter base, first lady Michelle Obama visited Colorado Thursday to rally for the Democrat.
"In order to have [Obama's] back, we're going to need to have people like Michael. We're going to need you again, and we're going to need you just as fired up and ready to go as two years ago," the first lady told the crowd.
Early voting ballots were mailed out to voters Tuesday and early results should start trickling in by next week.
ABC News' Mary Bruce contributed to this report.