Holt hits Booker as 'no progressive' in first ad

The ad riffs off of Holt's experience as a scientist and teacher and features him in a chemistry classroom, talking about policy proposals he says Booker opposes, including a carbon tax, breaking up big banks and banning government surveillance programs.

"I approved this message because Cory Booker may be the front-runner in this race, but he's no progressive," he says at the end.

The ad is running on the New York and Philadelphia broadcast and cable markets, and will air from Aug. 6-13, the day of the primary.

It's an attempt by Holt to make up some ground against Booker, who has a substantial lead in every poll of the race.

His Democratic opponents, including Rep. Frank Pallone (D) and state Assembly Speaker Sheila Oliver, have each come at Booker's seemingly ironclad lead at different angles. While Holt has characterized himself as the true progressive in the race, touting endorsements from progressive figures like Guardian reporter Glenn Greenwald, Holt has highlighted his modest background as a "typical Jersey story" against Booker's celebrity.

Booker is still heavily favored to win next Tuesday, however, and will likely take the seat in the October general election.