But the banning of Nadezhdin signals the Kremlin’s further shift from democracy to a system that Russian analysts describe as authoritarian, bordering on totalitarianism, where manipulated elections are used to provide a thin veneer of legitimacy for the 71-year-old president, without threatening his power.

This man wants to run against Putin. Thousands of Russians are helping him.

Russian authorities have previously barred any candidate who poses a real threat to Putin, such as the jailed opposition leader Alexei Navalny, admitting only a handpicked coterie of candidates who cooperate with the regime.

There are still three other candidates, but they are known to have few differences with the president and have a history of cooperation with the Kremlin. They are not expected to pose a significant challenge to Putin.

“Participating in the presidential election in 2024 is the most important political decision of my life. I am not backing down from my intentions,” said Nadezhdin, vowing to appeal the decision in court, a move unlikely to reverse the ban given the highly politicized nature of the court system.

The popularity of Nadezhdin’s candidacy took the Kremlin by surprise when long lines formed outside his election offices across Russia, indicating the depth of discontent over the war against Ukraine and other issues.

Nadezhdin, 60, a physicist and opposition politician, has often appeared on state television criticizing the war but does not have the high profile of other major opposition figures such as Navalny.

In a message on Telegram, Nadezhdin urged his supporters not to give up.

“Something has happened that many people could not believe in: Citizens have sensed the possibility of change in Russia,” he wrote.

Under Russian electoral law, a candidate must gather more than 100,000 signatures across the country to qualify. Nadezhdin submitted nearly 105,000, but the election commission rejected more than 9,100 of them, or 8.7 percent. To qualify, no more than 5 percent can be invalidated.

The commission claimed that the names of 11 dead people were found among his signatures and said this had tainted his entire list.

Nadezhdin’s team earlier reported that the commission’s automated software had misread the handwritten addresses of some signatories and disqualified them erroneously.

“You’re not denying me. You’re denying tens of millions of people who are hoping for change,” Nadezhdin said after the decision. “There are tens of millions of people standing here who were going to vote for me. I’m second after Putin. I’m gaining double digits in the polls, and you’re telling me about 11 dead people.”

Nadezhdin said he had collected more than 200,000 signatures, not all of which were submitted. “We conducted the collection openly and honestly. The queues at our headquarters and collection points were seen by the whole world.”

While the antiwar candidate does not appear to have the support to defeat Putin, a large protest vote in his favor and against the war would roil the Kremlin and could create internal divisions and unease about an increasingly unpopular war that has led to massive casualties and no clear benefits to ordinary Russians.

Opinion polling by independent pollster Levada in October found that 55 percent want to see peace talks, compared to 38 percent who want Russia to fight on.

Kremlin spokesman Dmitry Peskov said Nadezhdin was barred from running because of “a large number of errors in signatures, invalidation of a large number of signatures.”

“So an important criterion has not been met here. So I have nothing to comment on. The Central Election Commission strictly follows the rules that are set for candidate.”

In December, authorities barred another antiwar candidate, former television journalist Yekaterina Duntsova, from running in the election, after rejecting the signatures that she had submitted.

Critics have pointed to a number of other flaws in the election that could enable potential fraud. The vote will be held over three days, with an opaque system of electronic voting poised to play a central part for the first time.

The Kremlin dominates Russian media and opposition activists and critics of the war have been jailed. Employees of Russian state-owned enterprises are routinely required to show their bosses screenshots or cellphone photographs to prove that they have voted, and for whom.

Natalia Abbakumova in Riga, Latvia, contributed to this report