Rep. Cory GardnerCory Scott GardnerRepublicans jockey for position on immigration Bipartisan bill would toughen North Korea sanctions, require Trump's strategy GOP senators push for delay of ObamaCare insurer tax MORE (R-Colo.) accused Sen. Mark UdallMark UdallDemocratic primary could upend bid for Colorado seat Picking 2018 candidates pits McConnell vs. GOP groups Gorsuch's critics, running out of arguments, falsely scream 'sexist' MORE (D-Colo.) of lying about ObamaCare.

Gardner is challenging Udall in the midterm election for Udall's Senate seat.

“Mark Udall promised if you liked your plan, you could keep your plan," Gardner said on Thursday. "Mark Udall promised if you liked your doctor, you could keep your doctor. Mark Udall lied to the people of Colorado.”

Gardner has used Udall’s vote for the Affordable Care Act, also known as ObamaCare, against Udall in previous ads.

In the latest ad, Gardner points out that more than 300,000 Coloradans received healthcare cancellation notices, but he doesn’t say how many of those people now have insurance through the healthcare exchange.

Udall is one of the more vulnerable incumbents in November’s midterm election. Republicans need to win six Senate seats to gain control of the chamber.