One of the most prominent national gun control advocacy groups will be spending big to support Democratic U.S. Senate candidate John Hickenlooper, and another has endorsed the former Colorado governor, who is challenging Republican U.S. Sen. Cory Gardner.

Giffords PAC, the group founded by former Democratic Rep. Gabrielle Giffords of Arizona, has reserved $1.25 million in spending in the Colorado Senate race for TV ads scheduled to start airing at the end of the month, a spokesman told Colorado Politics.

“Senator Cory Gardner forgot he represents Coloradans – not President Trump and his NRA cronies,” said Peter Ambler, executive director of the Giffords organization. “Giffords PAC will remind voters who Gardner really listens to on gun safety reform. The days of Cory Gardner being able to dodge his record as a lackey for Trump and the gun lobby are over. This campaign will help power gun safety champion John Hickenlooper to the Senate.”

Giffords endorsed Hickenlooper in early March at an event in Aurora, held shortly before the state began to shut down due to the growing coronavirus pandemic.

The group spent more than $500,000 last year on advertising aimed at Gardner, pressuring the Republican to support background-check legislation passed by the Democratic-controlled House but stalled in the Republican-controlled Senate.

Brady PAC, the sister organization of Brady, the nation’s oldest gun violence prevention group, endorsed Hickenlooper last week, and a spokesman said the organization plans to spend big in the race.

“Brady PAC and Governor Hickenlooper have a shared goal to flip the Anti Gun Violence Prevention Majority and it starts by defeating Cory Gardner,” Brian Lemek, executive director of Brady PAC, told Colorado Politics in a statement.

“Time and time again Gardner and his Senate colleagues have avoided introducing legislation that could save countless lives, the most egregious being expanded background checks legislation that has passed the House and is supported by over 90% of Americans. We know, with Hickenlooper in the Senate, working to pass life saving legislation, Coloradans and all Americans will be more safe – which is why Brady PAC is proud to endorse him and plans to put our full weight behind Gov. Hickenlooper in this race.”

Hickenlooper has also won endorsements from sister organizations Everytown for Gun Safety Action Fund and Moms Demand Action.

Hickenlooper signed controversial legislation to require background checks and ban high-capacity magazines in 2013, in the wake of the 2012 Aurora theater shooting and a mass shooting later that year at an elementary school in Newton, Conn.

Opponents of the legislation recalled two Democratic state senators from office, and a third Democrat resigned her Senate seat in the face of a threatened recall.

While Hickenlooper has made the legislation a focus of his campaign, critics have questioned his enthusiasm at the time, pointing to a recording of the then-governor telling a meeting of Colorado sheriffs that he might not have signed the magazine limit if he’d known it would cause so much controversy.

Gardner has been the beneficiary of nearly $4 million in campaign contributions and spending by the NRA over his congressional career, but his supporters cite his legislative work to address mental health issues and authorize federal school safety grants.