Tensions between former South Bend Mayor Pete Buttigieg and former Vice President Joe Biden, both of whom are working to cultivate a base of moderate Democratic voters, are heating up.

On Saturday, Biden released a biting ad that is openly dismissive of Buttigieg’s record as a small city mayor, unfavorably comparing Buttigieg’s efforts to improve South Bend’s infrastructure with Biden’s accomplishments in the Senate and White House. The ad also highlighted controversies Buttigieg has faced with South Bend’s black community.

The message of the commercial was clear: Serious, executive branch work can’t be compared to the frivolity of small-city governance, and voters should choose the candidate with experience with the former.

Former Mayor Pete doesn’t think very highly of the Obama-Biden record. Let’s compare. pic.twitter.com/132TB7MHaq — Joe Biden (Text Join to 30330) (@JoeBiden) February 8, 2020

The Buttigieg campaign responded to the ad shortly after its debut. Chris Meagher, Buttigieg’s national press secretary, said in a statement that residents of small cities like South Bend “don’t think their lives are a Washington politician’s punchline.”

“The Vice President’s decision to run this ad speaks more to where he currently stands in this race than it does about Pete’s perspective as a mayor and veteran,” Meagher added.

Senior Biden campaign adviser Symone Sanders replied, “Joe Biden started life as an elected as a county councilman. He knows the power of local government. So he knows what mayors CAN do. The question here is what HAVE you done and are you ready to be commander in chief on day one?”

From there, the rhetoric between the candidates only intensified, with both men attacking each other in interviews broadcast Sunday.

Sunday morning, Buttigieg echoed his secretary, telling Jake Tapper on CNN’s State of the Union that communities like his are tired of being “punchlines” in Washington.

“We know we might look small from the perspective of Washington, but to us what’s going on in Washington looks so small or small-minded,” the former mayor said. “And communities, whether they’re my size, or rural communities, or even neighborhoods in our biggest cities that feel completely left behind, are frustrated with being made into a punchline by Washington politicians.”

On ABC’s This Week, Biden underscored that he believes Buttigieg is “a smart guy” who is simply too inexperienced to be president, and tried to explain how he sees the former mayor’s limited record as being different that Barack Obama’s in 2008.

“Who has he pulled together? Does he know any of the foreign leaders?” Biden asked. “Barack Obama came from a large state. He was a United States senator, he had run before. He’d been involved in international — he had a clear vision of what he thought the world should look like and so on.”

It’s a point Biden has made more succinctly before, saying Saturday, “This guy’s not a Barack Obama,” a statement Buttigieg was asked about on CNN Sunday.

“He’s right,” Buttigieg said when asked about the quote. “I’m not. And neither is he.”

“He’s right, I’m not, and neither is he,” Pete Buttigieg tells @jaketapper when asked to respond to Joe Biden’s comment that “this guy's not Barack Obama” https://t.co/H9i18W6F1H #CNNSOTU pic.twitter.com/wEqM5SbQDi — State of the Union (@CNNSotu) February 9, 2020

The Biden-Buttigieg dispute helps to clarify the differences between them

The underlying philosophies of the Biden and Buttigieg campaigns have always been in tension, but that those differences appear to now be boiling over reflect a changing dynamic in the presidential race.

Biden has been the national frontrunner since before he began campaigning, and while he still leads in averages of national polls, his standing has been damaged by a disappointing fourth place finish in Iowa as well as New Hampshire polls that suggest he’ll do poorly there as well.

And amid all of the chaos and confusion in Iowa last week, it was Buttigieg of all of Biden’s rivals who surged past him, to finish something like first.

That momentum does not appear to be limited to Iowa, either. According to the most recent polls out of New Hampshire, Buttigieg has picked up substantial support there — support that seems to come directly out of Biden’s camp. And the two have always vied for the same sort of voters, courting independents, centrist and conservative-leaning Democrats, and older voters.

Biden, of course, polls far better than Buttigieg with voters of color; Buttigieg consistently receives 2 percent or less support from African American voters, while Biden typically leads the pack among that group, with support hovering around 25 percent.

Black and Latinx voters will play a much larger role in upcoming contests in South Carolina and Nevada, and in many of the states participating in Super Tuesday, which is less than a month away. It is thanks to poll results in more diverse states like South Carolina and Nevada that Biden remains in the lead nationally, but before he can get to those races, he needs to finish the primary in New Hampshire — and could use a better than expected finish to pick up some momentum.

The fact that the two campaigns have begun to engage more directly suggests each has begun to view the other as its primary competition for votes, and that they hope to be able to win over New Hampshire voters in the eleventh hour — a strategy that may bear fruit given a recent CNN poll found nearly half of New Hampshire voters to be uncommitted.

And for those voters who have yet to make up their minds, the dispute between the campaigns should help to sharpen the contrast between them. Buttigieg and Biden share a fairly similar —and progressive — approach to policy. All of this weekend’s rhetoric, then, clarifies the choice voters considering both men have to make: Whether they want a familiar candidate with lots of Washington experience, or a fresh face with no federal government experience, but a strong connection to the Midwest.