But the ad, which will begin airing Tuesday in Des Moines and Cedar Rapids, does not describe South Bend, Indiana, Mayor Pete Buttigieg.

"No, not that guy," the narrator says, as an image of Buttigieg flashes on screen. "It's Cory Booker."

Although Buttigieg is most often mentioned as a recipient of the prestigious Rhodes scholarship, Booker is the "Rhodes Scholar mayor" who "has what it takes to beat Donald Trump," a narrator says in the ad

The spot plays off a memorable moment in the most recent Democratic debate , when Booker referred to himself as "the other Rhodes Scholar mayor on this stage," in a not-so-veiled nod to Buttigieg.

The ad is being bankrolled by United We Win , a super PAC that plans to spend $1 million to help Booker qualify for the December debate. Now that Booker has surpassed the DNC's 200,000-donor threshold, the group is shifting its focus to a two-week sprint to help boost his polling.

But the group's television ad seems to recognize what has been evident in recent polling: that Buttigieg is surging in Iowa as the alternative to former Vice President Joe Biden, shrinking Booker's path there. Booker and his allies hope to make the argument more sharply that he is the only candidate who could bring together all Democrats, including minority voters, and win in November 2020.

"Iowa Democrats want to support a leader with a vision for our country's future, and a Rhodes Scholar mayor is exactly what we need -- but Cory Booker is the only one with a record of delivering real change both in Washington and in his own community," said United We Win spokesperson Philip Swibinski. "Our party needs to rally around a candidate with a progressive platform and a pragmatic, results-oriented outlook in order to beat Donald Trump. Cory Booker exemplifies those qualities better than any other candidate, whether they're a fellow Rhodes Scholar mayor or not."

Booker reacted on CNN's "Situation Room" on Friday, saying he was caught "a little off-guard" by the ad, but that he has sought to run a unifying, positive campaign.

"I celebrate the people who are in the race," Booker said, "and my campaign is not about tearing anybody down."

Booker's campaign announced earlier this week that it would shift its "entire campaign apparatus into a persuasion effort " in order to net Booker the four polls he needs by Dec. 12 to secure a spot on the debate stage, reflecting the importance of this marker in the campaign's survival.

But while the campaign plans to spend six figures on digital and radio ads as part of that effort, it concluded that it could not afford to go up on television -- a hole that United We Win is stepping in to fill.

United We Win plans to initially spend $50,000 buying television time for the ad, a source familiar with the group's plans told CNN -- but the group expects that investment to go up. That spend will be part of a $200,000 investment in an "Iowa Week of Action," which will also include digital advertising and a call program focused on the key caucus state.