Sen. Mark UdallMark UdallElection autopsy: Latinos favored Clinton more than exit polls showed Live coverage: Tillerson's hearing for State The rise and possible fall of the ‘Card’ in politics MORE (D-Colo.) is again hammering his Republican opponent, Rep. Cory GardnerCory GardnerAngst in GOP over Trump's trade agenda GOP loses top Senate contenders Graham: Ryan tax plan won’t get 10 votes in the Senate MORE, for supporting restrictions on abortions and birth control in a new ad.

It’s the latest back-and-forth over Gardner’s support of a so-called “personhood” measure, which would have given legal rights to a fertilized human egg, effectively outlawing abortion and certain forms of birth control. And in a sign of how damaging Udall’s focus on the issue could ultimately become, Gardner hit back in a web video of his own.

In Udall’s ad, the senator says that Gardner “led a crusade that would make birth control illegal, and sponsored a bill that would make abortion a felony.”

“His record is beyond troubling. It’s wrong. We’re talking about your rights, as women, as families, as Coloradans,” Udall says. 

Gardner has, since entering the race, shifted his position on a personhood initiative in Colorado and now says he's opposed, but he remains a co-sponsor of federal personhood legislation.

In his response video, Gardner admits that he changed his mind on the issue, but says he did so after listening to voters — something he says “Udall and President Obama can’t relate to.”

“Their takeover of health care is a disaster. We all know it. Yet Udall and Obama refuse to listen – while everyone else pays for it,” Gardner says in the ad.

The two are locked in a tight battle for the seat, which became more competitive with Republicans as issues with the ObamaCare rollout and Obama’s persistent unpopularity have contributed to a difficult climate for Democrats. Most polling of the race has shown a single-digit fight, with Udall slightly ahead.