A super PAC that was once aligned with Florida Gov. Rick Scott is launching a new television ad that goes after U.S. Sen. Bill Nelson.

The New Republican super PAC is spending $2.4 million to air an ad that contends Nelson has not accomplished anything during his lengthy time in office. The ad is scheduled to start airing next Monday.

The ad echoes criticism that Scott has already leveled at the incumbent Democratic senator by noting how much Nelson has been paid during his political career.

Scott’s Senate campaign has already spent more than $5 million on three different television ads. But those ads did not criticize Nelson directly.

This race against Scott is Nelson’s most serious challenge since he was first elected to the U.S. Senate in 2000.