"I'm a pro-choice candidate who has a proven record of being a director of Planned Parenthood," Bivens told The Hill in February. "Congressman Flake is on the opposite end of that spectrum, as one of the most anti-choice candidates out there."

Although the Bivens ad makes no reference to opponent in the Democratic primary, former U.S. Surgeon General Richard Carmona, there is little doubt the ad is aimed at the primary electorate. Bivens has been running behind Carmona in the polls, although a February survey from Public Policy Polling showed Flake beating both Carmona and Bivens by 11 points.

A former independent, Carmona served under former President George W. Bush and is running as a centrist who can appeal to Republican voters. Democrats in Washington see him as one of their best chances to flip a Senate seat, helping to stave off a potential GOP takeover of the Senate in November.

By running to the left of Carmona, Bivens is attempting to convince primary voters that he is the only true Democrat in the race.

"The Arizona voters are going to have a real choice between a fellow who is a lifelong Democrat … versus a fellow who is a Bush-Cheney supporter, contributor, and someone who served in that administration," Bivens said.

Flake has a primary challenge as well, although he has a commanding lead in the polls over businessman Wil Cardon, a former Flake supporter. Cardon also went on the air in Arizona on Monday with a two-week cable and broadcast buy worth $230,000.

—This story was posted at 12:51 p.m. and has been updated.

Watch the ad: