DENVER (AP) -- The Senate race in Colorado has shot toward the top of the nation's most competitive contests this midterm election year, giving the Democratic incumbent a tougher battle than he expected and Republicans a new pickup opportunity in their drive to win the chamber's majority.
Sen. Mark Udall responded to Rep. Cory Gardner's surprise challenge by quickly trying to define his opponent as an extremist.
"People will find my record is a mainstream record, and the more people look at Rep. Gardner's record they'll see he's out of the mainstream," Udall said last week on a Colorado radio station.
Gardner, meanwhile, is tacking to the center after four years representing a conservative, rural district in Congress. As Gardner scrambles to raise money and assemble a campaign staff, his allies have hammered Udall's support for President Barack Obama's health care law.
"Tell Sen. Udall to stop thinking about politics and start thinking about people," an announcer says in a $1 million ad buy paid for by Americans for Prosperity, the national tea party group financed by the billionaire Koch brothers.
The political dynamics reflect those of House and Senate campaigns across the nation this year, when all 435 House seats and 36 seats in the Senate are on ballots. Republicans need a six-seat gain to wrest control of the Senate from the Democrats. The House is expected to remain in Republican hands.
In Colorado, the extremist label is potent. Democrats have won every top-of-the-ticket race in the state since 2004 partly by attacking Republicans as out of the mainstream, especially on issues central to moderate suburban women who carry outsized influence in elections. The state is evenly split between registered Democrats, Republicans and independent voters.
Still, Udall, 63, has far from a clear ride to re-election. The national health care law is deeply unpopular in his state, with 60 percent of Colorado's registered voters opposing it, according to a Quinnipiac University poll last month. Republicans have also begun to criticize Udall for supporting an Obama administration nominee for an Interior Department post who they contend is hostile to the energy industry.
Generally, polls have shown Udall barely ahead of Republican challengers, almost all of whom have dropped out of the primary since Gardner announced.
Seth Masket, a political scientist at the University of Denver, said Gardner's shift away from giving legal rights to fertilized human eggs, or personhood, was a smart move.
"The personhood amendment is a great opportunity for him to demonstrate he's moderating without it having a great impact on public policy - it's not like this was going to become law," Masket said. "This is what happens when you have an officeholder from a very conservative district running statewide - he has to branch out to a very competitive state."
Sean Tonner, a Republican consultant in Denver, said it makes sense for Democrats to hit Gardner hard and fast, because more voters have made up their minds on the better-known Udall. He said both politicians will be hard to demonize. Gardner, 39, is likable and upbeat, Tonner said, unlike the angry Republican in the typical Democratic attack ad.
"Mark Udall looks like he's out of central casting for Western politician - he looks like he was born with a Patagonia jacket sitting on a 14er," Tonner said, referring to Colorado's fabled peaks over 14,000 feet.
Democrats acknowledge Gardner's sunny demeanor but argue that the voting record he compiled in his conservative district, anchored in the farm towns that dot the northeast corner of the state, will hamper him.
In the state Legislature, Gardner co-sponsored a bill to make it a felony for a doctor to perform an abortion except to save the life of the mother, with no exceptions for rape or incest.
Democrats see more fodder in Gardner's record since being elected to the House in the Republican wave of 2010. He supported banning federal funding for abortions except in cases of "forcible rape"; former Republican vice presidential candidate Paul Ryan's budget, which would transform Medicare into a voucher-like system; reversing an Obama administration decision granting relief from deportation to some people brought to the United States illegally as children; and the budget proposal that sparked last year's partial government shutdown.
Gardner had supported a "personhood" ballot measure in Colorado. That effort was overwhelmingly rejected twice at the polls, but supporting it was key to winning Republican primaries in Colorado. In Congress, he twice co-sponsored federal versions of the effort. But earlier this month, after Gardner's last significant opponent in the GOP Senate primary dropped out, he said he realized critics' arguments that the ballot measure could outlaw some forms of birth control were correct, and he withdrew his support.
Democrats have savaged Gardner for the reversal, arguing that he's an opportunist.
"He may be a likable politician, but I don't think that's enough," said Craig Hughes, a Democratic consultant. "Cory Gardner is a political beast, and people don't like that."