GEOFF BENNETT: Today, a member of NATO in the European Union took a step nearly unheard of.

That's throwing out the results of an election.

That's what happened in Romania, a country that's been vital to Ukraine's efforts against Russia and also hosts U.S. troops.

Romania's Constitution annulled the results because of what the sitting government calls a vast influence effort by a foreign actor to boost the candidacy of a candidate dubbed pro-Russian.

As Nick Schifrin reports, the effort was largely run on TikTok.

NICK SCHIFRIN: In 2024, when a Romanian strongman wants to prove his manhood, he goes on TikTok.

And Calin Georgescu's opponents say, if this campaign looks like the Kremlin's playbook, it's because he admires Russian President Vladimir Putin.

CALIN GEORGESCU, Romanian Presidential Candidate (through translator): Putin is a leader.

He loves his country.

NICK SCHIFRIN: Scorns NATO and Ukraine.

CALIN GEORGESCU (through translator): Ukraine is an invented state.

NICK SCHIFRIN: And dabbles in conspiracy theories.

CALIN GEORGESCU (through translator): Did man reach the moon?

I don't think so.

NICK SCHIFRIN: He was also largely unknown, one of 14 candidates running in Romania's presidential election.

On November 5, Georgescu polled under 1 percent.

Three weeks later, he won the first round with 23 percent.

Romania's government says that victory was thanks to foreign influence and, for the first time in the country's history, declassified intelligence documents that describe a -- quote -- "campaign to circumvent Romanian law" to boost Calin Georgescu's popularity.

And the government says that campaign relied heavily on a well-coordinated, popularity-boosting campaign on TikTok.

Romanian intelligence says tens of thousands of TikTok accounts suddenly activated right before the election, some after laying dormant for eight years, and -- quote -- "The activity of the accounts would have been coordinated by a state actor."

ANDREI MURARU, Romanian Ambassador to the United States: Georgescu was supported by a state that NATO describes as the most significant threat to NATO and Romanian security, and that state is Russia.

NICK SCHIFRIN: Andrei Muraru is Romania's ambassador to the United States.

ANDREI MURARU: There are many things that could be shaken if this guy would have become president, a puppet in the Russia's hands, which would be a disaster for our security, for our economy, for our alliances, and for our future.

NICK SCHIFRIN: Romanian intelligence describes a network of TikTok supporters, some paid by a shell company that soon disappeared, all instructed to post unified messages about what they want out of a leader, a family man, who's honest and patriotic.

These avoided Georgescu's name, skirting TikTok's own policies against political content.

Instead, they relied on hashtags and an army of bots to leave pro-Georgescu comments, playing into TikTok's algorithm and spreading throughout Romania.

ANDREI MURARU: At least one TikTok account used by Romanian citizens to promote candidate Georgescu on social media was financed with over one million euro.

NICK SCHIFRIN: Secretary of State Antony Blinken earlier this week: ANTONY BLINKEN, U.S. Secretary of State: And now Romanian authorities are uncovering a Russian effort, large in scale and well-funded, to influence the recent presidential election.

NICK SCHIFRIN: Local and U.S. authorities called out pro-Russian actors influencing recent elections in Romania's neighborhoods Moldova and using TikTok in last year's parliamentary elections in Bulgaria.

THOMAS REGNIER, Spokesperson, European Commission: TikTok needs to step up resources to counter information operations.

NICK SCHIFRIN: This week, parliamentarians in Europe challenged TikTok executives.

DIRK GOTINK, European Parliament: Ninety-five content moderators, 6,000 in Europe, what the hell were they doing during the elections?

CAROLINE GREER, Director of Public Policy and Government Relations, TikTok: Our line of sight goes to our platform and activity that is taking place on our platform.

We do not know what's happening offline.

NICK SCHIFRIN: Today, Georgescu described the decision to annul the first round and delay the second round as a state coup.

CALIN GEORGESCU (through translator): The rule of law is in and induced coma and justice is subordinated to political orders.

NICK SCHIFRIN: Some centrist parties also condemned today's constitutional court ruling and argued popular disaffection with the government opened the door to an outsider's campaign.

CLARA VOLINTIRU, German Marshall Fund of the United States: There was a very real networking process of mobilizing disenfranchised groups across the regions in Romania and across the diaspora.

NICK SCHIFRIN: Clara Volintiru is the director of the German Marshall Fund for the Black Sea region.

CLARA VOLINTIRU: Grievances from the regions, from rural communities, from categories of the public that don't feel they are taken seriously with regards to the decreased standards of living, with regards to their fears, uncertainties, traditional identities.

So there is a lot of fear that the Russian narratives are exploiting.

NICK SCHIFRIN: Today's court decision cannot be appealed.

But it hasn't blocked the appeal of Georgescu TikTok videos that continue to gain views.

For the "PBS News Hour," I'm Nick Schifrin.