A campaign visit from former President Bill ClintonWilliam (Bill) Jefferson ClintonCybersecurity for national defense: How many 'wake-up calls' does it take? Who's in control alters our opinion of how things are Obama adviser jabs Hillary Clinton over Monica Lewinsky comments MORE kept Colorado's Senate race in the national spotlight for another day Monday.

The Clinton rally for Sen. Michael BennetMichael Farrand BennetEagles player sits out national anthem Trump administration denied it has ‘secret’ committee seeking negative information on marijuana: report Overnight Health Care: Senators target surprise medical bills | Group looks to allow Medicaid funds for substance abuse programs | FDA launches anti-vaping campaign for teens MORE (D-Colo.) came as early voting got under way in the state and right on the heels of a "Meet the Press" debate between the two candidates, which grabbed some unwanted headlines for Republican Ken Buck. 

Clinton stumping for Bennet marks a turnaround from the Democratic primary in Colorado, where the former president not only backed challenger Andrew Romanoff, but bucked the White House to do it. 

Bennet's primary was at the top of the list for President Obama, with the White House desperate not to have another sitting Democratic incumbent lose a primary after receiving some high-profile public support from the president.

Bennet, who was appointed to the seat after Sen. Ken Salazar (D-Colo.) left to become secretary of the Interior, survived Romanoff, despite the challenger's backing and fundraising help from Clinton. 

The general-election race now stands near the top of priorities for the White House, given that another Senate seat in Illinois, also left vulnerable as a result of the president's election, could be poised to fall into GOP hands as well.  

On Monday, the former president warned Colorado voters about the presence of outside Republican groups spending on TV ads attacking Bennet, calling the groups "too chicken" to reveal their donors. 

The Buck campaign took a shot at Clinton's visit for Bennet, noting that it's the second time the former president has endorsed a Democrat in the contest. 

“We hope President Clinton’s second endorsement in the Senate race is just as successful as his first," Buck campaign spokesman Owen Loftus said in a statement. 

The latest Rasmussen poll in the race showed the contest tightening a bit with Buck ahead just two points, 47 percent to 45, as Democrats think Buck's stumbles this past Sunday in the "Meet the Press" debate will continue to dog him. 

The Republican called homosexuality a lifestyle choice and appeared to compare being gay to alcoholism. After the debate, Buck attempted to clarify his remarks, telling reporters he wasn't suggesting being gay is a "disease."

"I said I thought there was some element of predisposition, and I thought there was some element of choice," Buck said on his comments on homosexuality. "I'm not a biologist, and I haven't studied the issue, but that's my feeling on the issue."

The Bennet campaign jumped on the remarks quickly afterward and has kept up the pressure on that issue and questions over a 2005 case of alleged rape that Buck declined to prosecute. 

Ultimately, this race is expected to be one of the tightest Senate contests in the nation come Election Day, and it offers a good test of just how quickly an association with Washington and Obama can drag a candidate down this year.

Bennet has found himself pushing back against the claim that he's nothing more than a creature of Washington with the mentality of a career politician, despite having spent less than two years in a Senate seat he wasn't even elected to. 

Bennet did vote yes on healthcare reform and the stimulus, two votes that polling suggests have hurt him with independent voters and left him a hurdle to climb ahead of Election Day. 

It's also a significant race and state for the president in another sense — Colorado was one of the states Obama was able to turn a deep shade of purple in 2008 thanks to support from independents and centrist Democrats. A loss here would further cement the independent shift away from President Obama and national Democrats in a key battleground state.    

The race also offers a good test of the Obama-vs.-Clinton dynamic when it comes to campaign support. A new Gallup poll out Tuesday confirms what vulnerable Democratic lawmakers have known for months — that former President Clinton's presence on the midterm campaign trail is more helpful than Obama's. 

Among Democrats, 48 percent said a visit from Obama would in fact make them more likely to vote for a candidate. But 52 percent of Democrats said the same of a visit from Clinton. 

The most striking difference came among Republicans and independents. A full 71 percent of Republicans said an appearance by Obama would mean they would be less likely to vote for the candidate he stumped for, while just 46 percent felt the same way about a Clinton visit. 

For independents, there was a similarly large gap, with most saying a visit from either Clinton or Obama won't make a difference at all in their vote choice. But 39 percent of independents said an Obama visit would hurt a candidate's standing with them, while just 23 percent said the same of a Clinton visit.