Skeptics abound, and many question whether Ms. Sobchak is opposing the current czar or doing his bidding. Every recent presidential election has featured a high-profile liberal candidate handpicked by the Kremlin. Hence some accuse her of being a spoiler to undermine the campaign of Aleksei Navalny, an anticorruption campaigner who has spent more than a year organizing a presidential bid.

Ms. Sobchak denies that, and suggests that voters want an alternative to the confrontations and street demonstrations promoted by Mr. Navalny. “When you go with very radical slogans, you only make people more angry,” she said, with unpredictable consequences. “Revolutions in Russia are even worse than bad czars.”

By making “Against Thieves” part of her campaign slogan, she has adopted part of Mr. Navalny’s platform. But there were obvious differences. Ms. Sobchak flew in on business class and arrived at the venue in a chauffeured black Mercedes an hour late, after stopping to get her hair done.

Her crowds seemed sparser and less energetic than Mr. Navalny’s, though she has siphoned off some Navalny supporters. “Navalny will not be allowed to register, and I want to take part in the vote,” said Andrei Sotskov, a 53-year-old boxing coach. “I have heard her called a spoiler, but there is nothing to prove this theory.”

Other critics on the left condemn her for focusing on the “system” rather than more bluntly on Mr. Putin and legitimizing what they consider a sham by running.

“What is the goal of running against a candidate with 100 percent chance of success?” wrote Karina Orlova, a Russian journalist, in a blog post.