If there was ever a Biden-Buttigieg cold war, it just got hot.

For months, former Vice President Joe Biden and South Bend Mayor Pete Buttigieg have avoided any major direct confrontation during the sporadic gloves-off skirmishes of the Democratic primary. Biden, the former chairman of the Senate Foreign Relations Committee, and Buttigieg, a veteran of the Afghanistan war, have each sought to make cogent commander-in-chief cases on the campaign trail—hardly ever at each other’s expense.

But with just over a month until caucusing commences, the unpredictability of the political cycle has turned the notion of an inevitable winner upside down, with two of the leading contenders—a 77-year-old established politician and a 37-year-old Beltway neophyte—now on a collision course over one of their most powerful shared interests.

The two men have markedly different approaches to highlighting contrasts with their rivals. Biden, who has reliably topped national polls since launching his campaign in April, tends to employ a simple approach: Stay (mostly) out of the fray; attack (mostly) only when attacked; and try, with varying degrees of success, to stick to the script.

Buttigieg, whose final term as mayor of South Bend, Indiana, officially ends at noon on Wednesday, prefers the opposite. When Sen. Elizabeth Warren (D-MA) hesitated for weeks to release financial details of her health care proposal, for example, the mayor made sure to note that resistance during a televised debate in front of millions of viewers. When Warren hit back in a subsequent event for Buttigieg’s frequent appearance at high-dollar fundraisers, he reminded viewers she’s the “wealthy person” — not him.

Now, with the two moderate Democrats just three percentage points away from each other in Iowa and New Hampshire, the first two early voting states that tee off the nominating contest in mere weeks, Buttigieg has gone on a rare offensive against Biden. The mayor has criticized the former senator’s Iraq War vote—a favorite line of attack from Sen. Bernie Sanders (I-VT), who was opposed to the effort—and changed his tone on Biden’s son Hunter, who has been the subject of a coordinated misinformation campaign from President Donald Trump.

“As I’ve said before, I don’t think it’s a smart strategy because those who have gone after the VP on the Democratic side have not lived politically to tell about it,” Antjuan Seawright, a Democratic strategist familiar with Biden’s early state operation in the South, told The Daily Beast.

One person directly familiar with Biden’s thinking framed it more broadly.

“The closer you get to voting, the more pot shots you take,” the insider said. “He’s seen his numbers go down. We’ve seen this with [Sen. Kamala] Harris up and down, Warren up and down, and Buttigieg. Campaigns and candidates at some point kind of can’t help themselves.”

“ I certainly respect the vice president, but this is an example of why years in Washington is not always the same thing as judgment. ” — Pete Buttigieg

The insider’s comments were made in reference to Buttigieg calling the Iraq War the “worst foreign policy decision made by the United States in my lifetime” in an interview with Iowa Public Television on Sunday.

“I certainly respect the vice president, but this is an example of why years in Washington is not always the same thing as judgment,” Buttigieg said.

Buttigieg, who unlike Sanders did not say the vote was disqualifying, is unlikely to make Biden’s Iraq War stance a focus of his offensive strategy but rather one data point in a larger thread of contrast among multiple contenders. Indeed, the Buttigieg campaign is more keen to double down on the previous line of contrast that’s he’s been discussing publicly for months: that “Washington experience” isn’t the only type of relevant work history necessary to become president and that judgment is informed by many different personal and professional paths.

That theme is so well known that one campaign adviser affiliated with a separate rival candidate acknowledged strategizing around Buttigieg’s potential to bring up his military experience at some point on the debate stage.

“He had telegraphed this was going to be his set,” the source said.

In an interview on Monday, the mayor also weighed in on an issue that has infuriated Team Biden for months: his son Hunter Biden’s work in Ukraine. When asked by the Associated Press how Buttigieg would have handled a hypothetical politically delicate situation similar to Biden’s, he said he would have taken a different approach.

“I would not have wanted to see that happen,” Buttigieg said, in reference to Hunter serving on the board of a Ukrainian natural gas company while his father served as vice president. A moment later, Buttigieg reiterated previous remarks that the line of questioning is nothing more than a distraction. “At the same time, again, I think this is being used to divert attention from what’s really at stake in the impeachment process. There’s been no allegation, let alone finding of any kind of wrongdoing,” he said.

Still, Buttigieg’s criticism is a change in posture for the Indiana Democrat, who has defended the former vice president’s son in the face of an onslaught of harassment from Trump.

In an October appearance on CNN’s State of the Union, Buttigieg lauded Hunter Biden’s decision to step down from the board of a Chinese private equity company, citing it as an improvement on the Trump administration’s embrace of nepotism.

“I think it demonstrates the difference in standards relative to the White House,” Buttigieg said at the time. “I mean, here you have Hunter Biden stepping down from a position in order to make sure, even though there’s been no accusation of wrongdoing, doing something just to make sure there’s not even the appearance of a conflict of interest. While, in the White House, the president of the United States is a walking conflict of interest.”

That same month, Buttigieg dodged a question from the Washington Examiner about whether he would allow his own child to serve on the board of a foreign company, calling the issue a “shiny object” intended to divide the Democratic Party and deflect from the president’s own actions.

“One thing that is really important right now is to deny this president [the opportunity] to change the subject, and the subject is that the president confessed on national television to an abuse of power,” Buttigieg said at the time. “Let’s deal with that and not get caught in the shiny objects he’s going to throw out.”

The change of tone now matches the frenetic nature of the Democratic primary cycle, multiple campaign insiders and outside strategists said, when several candidates all competing for momentum in the first few early voting states throw out new lines of contrast in an effort to maximize attention.

This week’s remarks were not the first time Buttigieg signaled differences with Biden over foreign policy. In June, The Daily Beast reported early signs of the mayor quietly moving in on one of Biden’s top issues: America’s standing on the world stage. During competing campaign events on the same day, both Democrats used the word “existential” when discussing matters of national security, both arguing that the fundamental principle of democracy was under attack by Trump and highlighting parts of their own records to put the country back on track.

Spokespeople from Biden’s and Buttigieg’s campaigns declined to comment on the record for this story. But as the Feb. 3 Iowa caucus approaches, Democratic strategists eagerly gamed out the polling implications of reigniting such contrasts again now.

“A well-run campaign, which we have every reason to believe Buttigieg’s is, wouldn’t be attacking Biden unless their internal data showed it was necessary,” one Democratic strategist said. “Likewise, they would only use a message that quantitative or qualitative data showed had a chance at success.”

The latest Real Clear Politics polling average reveals a hefty gap between Biden and Buttigieg’s standing nationally. The former vice president has a commanding 20-point lead over Buttigieg, earing 28.4 percent of support to the mayor’s 8.2 percent. In the early states, the space between the two aspirants is much narrower. In Iowa, where Buttigieg has surged in recent months, he tops polling averages at 22 percent. But Biden, who has focused the majority of his campaign strategy on winning more diverse areas, including South Carolina, is just behind Buttigieg at 18.8 percent, following an eight-day, 18-county bus tour there. In New Hampshire, it’s a similar story. Buttigieg is approximately three points ahead of Biden there, earning 17.7 percent of support to the former vice president’s 14.3 percent. Both of them trail Sanders, with 19 percent.

“I think Pete is worried he will lose voters to Biden,” Liz Mair, a veteran Republican campaign operative, said simply.

Still, other seasoned political hands offered a more optimistic end result for Buttigieg, who one former top campaign aide to Hillary Clinton said “isn’t afraid to go on offense,” suggesting that’s a strategic advantage in a matchup against Trump.

“The difference between what we are seeing from him and have seen from others in the past is that if he isn’t the nominee, he will be at the front of the line to unite the party,” the former Clinton aide said.