In late 2021, as he prepared to make a second run for a suburban New York City House seat, George Santos gave permission for his campaign to commission a routine background study on him.

Campaigns frequently rely on this kind of research, known as vulnerability studies, to identify anything problematic that an opponent might seize on. But when the report came back on Santos, the findings by a Washington research company were far more startling, suggesting a pattern of deception that cut to the heart of the image he had cultivated as a wealthy financier.

Some of Santos’ own vendors were so alarmed after seeing the study in late November 2021 that they urged him to drop out of the race and warned that he could risk public humiliation by continuing. When Santos disputed key findings and vowed to continue running, members of the campaign team quit, according to three of the four people The New York Times spoke to with knowledge of the study.

The episode, which has not been previously reported, is the most explicit evidence to date that a small circle of well-connected Republican campaign professionals had indications far earlier than the public that Santos was spinning an elaborate web of deceits and that the candidate himself had been warned about just how vulnerable those lies were to unraveling.

Fraudulent academic degrees. Involvement in a company accused of a Ponzi scheme. Multiple evictions and a suspended driver’s license. All of it was in the report, which also said that Santos, who is openly gay, had been married to a woman. The report did not offer conclusive details, but some people briefed on the findings wondered whether the marriage was done for immigration purposes.

It remains unclear who else, if anyone, learned about the background study’s contents at the time or if the information made its way to party leaders in New York or Washington. Santos, 34, managed to keep almost all of it from the public until after he was elected, when an investigation by the Times independently unearthed the problematic claims documented by researchers and others that they missed.

After the Times sent a detailed list of questions for this story, a lawyer for Santos, Joe Murray, said, “It would be inappropriate to respond due to ongoing investigations.” A spokesperson for Santos’ congressional office did not respond to a similar request for comment.

Santos himself has admitted to some fabrications but insists he was merely embellishing his qualifications. He has vowed to serve out a two-year term in Congress. State, local and federal prosecutors now are investigating his activity.

The existence of the vulnerability study underscores one of the most vexing questions still surrounding the strange saga of Santos: How did the gatekeeping system of American politics — Republican leaders, adversarial Democrats and the prying media — allow a fabulist who boasted about phantom mansions and a fake résumé get away with his con for so long?

Interviews with more than two dozen associates, adversaries and donors, as well as contemporaneous communications and other documents reviewed by the Times, show that Santos inspired no shortage of suspicion during his 2022 campaign.

Well-connected supporters suspected him of lying and demanded to see his résumé. Another former campaign vendor warned a state party official about what he believed were questionable business practices. And the head of the main House Republican super political action committee told some lawmakers and donors that he believed Santos’ story did not add up.

But in each case, rather than denounce Santos publicly, the Republicans looked the other way. They neglected to get the attention of more powerful leaders and allowed him to run unopposed in the 2022 primary.

Some assumed Santos’ falsehoods were garden-variety political embellishments; others thought Democrats would do their dirty work for them, and Santos would be exposed in the heat of a general election campaign.

But Democrats struggled to do so. In 2020, the party incumbent, Tom Suozzi, dismissed Santos as a nonviable threat and conducted no opposition research at all while cruising to victory. When Democrats did vet him two years later, they failed to find some of the most egregious fabrications.

Democrats then labored unsuccessfully to persuade the news media, which had been weakened by years of staff cuts and consumed by higher-profile races, to dig into the troubling leads they did unearth. Aside from The North Shore Leader — a small weekly newspaper on Long Island, which labeled Santos “a fake” — and a few opinion pieces in Newsday, New York’s media machine paid Santos scant attention.

Santos was a political neophyte when he first showed interest in running for a House seat made up of parts of Queens and Nassau County in 2020. His only real electoral experience ended quickly: A year earlier, he was forced to drop his insurgent campaign for a low-level party position in Queens because he lacked enough valid signatures to make the ballot. Among the tight-knit Republican circles on Long Island, he was virtually unknown.

In normal circumstances, Santos would have been shooed away. Republicans in Nassau County, which comprises the bulk of New York’s 3rd Congressional District, long have been famous for exercising tight control over who runs.

But with the country in lockdown in the early days of the coronavirus pandemic and the district expected to remain under Democratic control, no one else put his hand up to run. Santos submitted a résumé and answered a vetting questionnaire riddled with lies, including that he had a 3.9 grade-point average from a college he never graduated from and job credentials he did not possess. A vetting team for the county Republican Party accepted his answers without question.

When Santos chose to run again two years later, local Republicans again gave him their support. They expected that flipping the district would again be a stretch.

There were already questions swirling by that time among donors and political figures about where exactly Santos lived and the source of the money that supported the lavish lifestyle he boasted about.

In summer 2021, one of the former advisers to Santos, who insisted on anonymity, discovered his connections to Harbor City Capital, the Florida-based company accused of a Ponzi scheme, and to other suspicious business practices that Santos had obscured. The adviser said he took the findings to a state party official later that fall and tried to pitch the story to a newspaper, which he said did not pursue it.