Americans for Prosperity will launch a new three-week ad attack on Monday against Sen. Mark Udall of Colorado, making him the latest vulnerable Democratic incumbent to be targeted by the group.

The ad will point to Udall’s support of the Affordable Care Act and will run across the state on cable, network and digital platforms. The troubled rollout of the president’s signature health-care law has been damaging to Udall, weakening his poll numbers in the swing state.

The $970,000 buy is the first the group has made statewide in Colorado this cycle and comes just weeks after Rep. Cory Gardener (R-Colo.) announced his challenge to Udall, clearing the Republican field and setting up a hotly contested race in 2014.

“Because of the nature of the vote as it occurred in the Senate, he cast the decisive vote,” AFP President Tim Phillips said. “If he had just voted no, this law wouldn’t be a reality today for so many Americans.”

The group will also announce a new round of television ads against Sen. Mary Landrieu (D-La.) on Monday. The $700,000 buy is the latest in a series of attacks slamming Landrieu’s support of Obamacare.

The latest ad buys are part of a multimillion-dollar campaign by the Koch-brothers-backed nonprofit group to eventually repeal the president’s health-care law.