SOUTH BEND, Ind. — Caught off guard by his sudden surge, Pete Buttigieg's rivals are scrambling to find vulnerabilities and lines of attack that can be used against him, five officials with opposing Democratic primary campaigns and Republican political groups tell NBC News.

The situation is different than with Bernie Sanders, Elizabeth Warren and Joe Biden, Democrats who have long been on the national scene and were widely expected to run for president. Potential rivals and GOP campaign groups have spent years hunting for dirt — known in political parlance as "opposition research" — that could be deployed against them. Major political groups had entire books of "oppo" ready to go by the time those candidates entered the race. Biden is expected to enter formally this week.

In contrast, Buttigieg was on nobody's radar as a serious presidential contender until a few weeks ago. As a millennial who has never held an office higher than mayor of a midsize town, his record is largely unexamined.

Now his competitors are rushing to file a flood of Freedom of Information Act requests, according to officials, collecting everything he's ever said in public or posted on social media, and poring over years-old budgets from South Bend, Indiana, where he's served as mayor since 2012.

One official from a rival Democratic presidential campaign described Buttigieg as "a 37-year-old kid mayor, who nobody knows anything about."

"He's getting a very significant free pass on a lot of stuff that other candidates aren't getting a free pass on," the official said, citing his willingness to take money from lobbyists as an example. "There's a novelty there. People don't know anything about him, so he can kind of be whatever people want him to be. But if he sustains this, that will come down to earth."

Until the last few weeks, the only group that had kept close tabs on Buttigieg and actively pushed back on him was the Indiana Republican Party. Officials said the state party took notice when Buttigieg in 2017 ran for Democratic National Committee chair, taking it as a sign that his ambitions extended beyond South Bend, population just over 100,000.

The Indiana GOP began opposing Buttigieg more aggressively in 2018, including criticizing his move that year to block the opening of a crisis pregnancy center that discourages abortion by overruling the municipal council's zoning decision. The state party has also worked to impugn his broader record as mayor, emphasizing high rates of violence and downplaying the significance of his electoral victories in South Bend, a comparatively liberal enclave within conservative-leaning Indiana.

Yet since Buttigieg starting attracting national attention, catapulting into third place in Democratic primary polls in Iowa and New Hampshire, the state GOP has been consulting with the Republican National Committee about ways to effectively counter Buttigieg's campaign, officials said.

Officials with rival Democratic campaigns said that while they're still early in the process of digging through his record, they've already identified his likely vulnerabilities. A few issues have already worked their way into national press coverage of Buttigieg, including a re-examination of a fraught episode in which he demoted the city's black police chief, detailed in recent New York Times and NBC News reports.

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"Our competitors can run their campaigns how they want," said Lis Smith, Buttigieg's top communications adviser. "We're less interested in politics as usual and more focused on getting Mayor Pete's hopeful message of generational change out there."

Other potential points of vulnerability include his signature project as mayor, the "1,000 homes in 1,000 days" initiative to rid South Bend of abandoned homes, and his years at McKinsey and Co., a business consulting firm that has drawn intense scrutiny from Democrats over some of its business practices. His opponents also plan to hit him on his reluctance to take definitive stances on policy issues like health care and immigration, officials said.

Colin Reed, a Republican strategist who specializes in opposition research, said any campaign competing with Buttigieg would be working expeditiously now to piece together his record as mayor, including every interview he ever gave, unpopular personnel decisions he made and any municipal correspondence in the public record. He said Buttigieg's work at McKinsey could be particularly ripe for "guilt by association" attacks given the current focus within the Democratic primary on "purity and corporate responsibility."

"In 2020 it was never going to be like 2016, where all the Republicans knew that Hillary Clinton was going to be the nominee and you essentially had four years to build a formidable opposition arsenal against her," said Reed, who constructed many of the earliest attacks on Warren as campaign manager for former Massachusetts Sen. Scott Brown. "There was always going to be a bit of this scramble."