Sen. Mark UdallMark UdallLive coverage: Tillerson's hearing for State The rise and possible fall of the ‘Card’ in politics Gardner's chief of staff tapped for Senate GOP campaign director MORE (D-Colo.) is airing his first ad of his reelection fight, a negative spot that hits Republican opponent Rep. Cory GardnerCory GardnerOvernight Tech: Tech listens for clues at Sessions hearing | EU weighs expanding privacy rule | Senators blast Backpage execs Overnight Tech: Trump meets Alibaba founder | Uber to make some data public | GOP Lawmakers tapped for key tech panels Iranian lawmakers vote to boost military spending MORE on abortion and other women’s issues.

The ad declares that Gardner’s “history promoting harsh abortion laws is disturbing,” and highlights "personhood" measures he’s supported that would have given legal rights to a fertilized human egg, effectively outlawing abortion and certain forms of birth control.

Gardner has, since entering the race, shifted his position on those measures and now opposes them, but Udall’s campaign has continued to knock him on the issue because he remains a co-sponsor of federal personhood legislation.

“But Mark Udall protects our right to choose, our access to birth control,” a female narrator says in the ad. “Mark Udall, in a word: Respect.”

Democrats believe women's issues in particular will help them take down Gardner, who entered the race in February and gave Republicans a top-tier challenger in a race they see as competitive due to ObamaCare.

Gardner’s campaign blasted Udall for going negative, with his campaign manager Chris Hansen charging the senator is attacking Gardner because “he has no record of accomplishments."

”While Coloradans sound the call for new leadership, Sen. Udall continues to lie about Cory Gardner’s record while distorting his own,” Hansen added.

He went on to knock Udall on ObamaCare, declaring that "if Senator Udall trusts and respects women, and all Coloradans for that matter, then he should not have lied to them about keeping their healthcare plans and doctors."