Romania’s top court on Friday annulled the country’s entire presidential election, citing declassified documents that showed the electoral process was spoiled through vote manipulation, campaign irregularities, and non-transparent funding. With documents pointing to Russian agents abusing the social media platform TikTok, it appears to be the first time in history that a presidential election has been stopped due to social media violations.

The documents indicate that a pro-Russian candidate, Calin Georgescu, benefited from an anonymous TikTok campaign, seeing his social media account surge to 6 million likes and 541,000 followers after being decidedly marginal as recently as September. Once a fringe candidate, Mr. Georgescu unexpectedly won the first round of voting, on November 24. One of 13 candidates, he finished with 23 percent of 9.4 million votes cast.

A Bucharest-based think tank, Expert Forum, reported that Mr. Georgescu’s account had an explosion in interest that “appears sudden and artificial, similar to his polling results.” It is unclear if the candidate will be allowed to run in the replay. Romania’s anti-organized crime prosecuting unit says it is investigating Mr. Georgescu’s campaign after analyzing the documents that purport to point to a Moscow-orchestrated web of thousands of TikTok and Telegram accounts.

Romania’s outgoing president, Klaus Iohannis, said Friday that a new government will set the date and conditions for a new presidential election. On Wednesday, a coalition government was formed comprising the four centrist parties that fared well in parliamentary elections on December 1. With his term expiring December 21, Mr. Iohannis said in a national TV address Friday that he will stay on until his successor is named.

Mr. Iohannis told this nation of 19 million people he was “deeply concerned” by the intelligence reports that indicated one candidate’s campaign was “unlawfully supported from outside Romania.” 

“The same candidate declared zero campaign expenditures, despite running a highly sophisticated campaign,” he said, referring to Mr. Georgescu, a soil scientist by training. “Intelligence reports revealed that this candidate’s campaign was supported by a foreign state with interests contrary to Romania’s. These are serious issues.” 

In a retort, Mr. Georgescu told Realitatea TV that the court’s ruling was an “official coup” and evidence of a corrupt system. Opinion polls indicated he was heading to victory in the second round of the election. With the main election scheduled for Sunday, voting already had started Friday morning at 951 polling stations abroad. 

In last Sunday’s voting, Mr. Georgescu’s former party, the hard-right Alliance for the Union of Romanians, doubled its seats in Romania’s two-chamber parliament, to 18 percent of the total. Two years ago, Mr. Georescu was kicked out of the party for praising President Putin and mocking the North Atlantic Treaty. NATO is building its largest European base in Romania, near the Black Sea port of Constanta. Today, the leader of this party, George Simion, said the election annulment was a “coup d’état in full swing.” Yet he urged people not to take to the streets.

Now, Romania faces its largest political crisis since the overthrow and execution of its communist dictator, Nicolae Ceaușescu, in 1989. 

A pro-European Union centrist leader, Elena Lasconi, excoriated the court’s ruling, saying she would have won the runoff vote this Sunday. She said: “The constitutional court’s decision is illegal, amoral, and crushes the very essence of democracy, voting.” 

She added: ‘“We should have moved forward with the vote. We should have respected the will of the Romanian people. Whether we like it or not, from a legal and legitimate standpoint, 9 million Romanian citizens, both in the country and the diaspora, expressed their preference for a particular candidate through their votes. We cannot ignore their will!”

The country’s Social Democrat prime minister, Marcel Ciolacu, who narrowly lost to Ms. Lasconi last month, supported the cancellation, calling it “the only correct solution.” He posted on Facebook: “The Romanian people’s vote was flagrantly distorted as a result of Russian interference.”

There was no official reaction from Moscow. Friday’s reversal in Romania comes as the Kremlin suffers another setback in Syria, where the al-Assad regime has been a close ally of Moscow for more than half a century. With Turkish-supplied rebels moving steadily south, the Russian Embassy at Damascus Friday called on all Russian citizens to leave the country immediately.

At the same time, video clips showed Russian trucks evacuating S-400 air defense systems to its port at Tartus. From there, they could be pulled out of Syria by ship. Sky News Arabia reports that Russia has told Damascus that any intervention to save the regime will be limited, presumably because Ukraine is Russia’s priority.