Does the opposition figure with the highest chance to challenge Putin always end up disqualified?

Question

In Russia, since Putin took [part in] power (say since 2000), is it always the case that opposition leaders that were attaining high popularity (relative to other opposition figures), or at least high momentum (rapid increase) in gaining such popularity, ended up out of the elections race, for various reasons, such as: getting a criminal dossier, getting killed, etc.?

Basically, I want a (brief) historical account of high-impact opposition figures and their [non-]participation in elections. Ideally, their popularity [or momentum in gaining such] should be confirmed with an opinion poll [or two]... assuming these are even possible in Russia. (If not, it would be interesting to hear briefly why these can't take place.)

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I'm asking in the context of Putin's declaration last year that he does not mind a credible opposition:

"As for your question about the opposition: why doesn't such [an opposition] emerge that would be competitive... The simplest thing for me to say would be that it's not up to me to raise competitors for myself," Putin said, speaking at his annual presser in Moscow December 14. At the same time, he noted that there must be competition in politics. "Although I must say something unexpected: I think that our political environment, as well as an economic one, should be competitive. And, of course, I would very much like - I want it and I will strive for it - that we have a balanced political system. And it is impossible to imagine it without competition in the political field," the Russian president said. "Why do we seem to have noisy and active opposition who are not a real competition for the current authorities? You know, to put it mildly, great peculiarities have developed in Russia over the past decades," he stressed.

Great peculiarities indeed. I can remember myself that Boris Nemtsov ended up assassinated (2015) and in 2017 Alexei Navalny was barred because of a previous fraud conviction. But were they the main figures of the opposition at the time, or just some guy in the pack? And does the list of "great peculiarities" extend further in time before these two?

Answer 1

US President Franklin Delano Roosevelt once said "In politics, nothing happens by accident. If it happens, you can bet it was planned that way". If there is a widespread harassment campaign against an opposition activist (in 2018 the main opposition figure Alexi Navalny had the biggest supporter base after Putin but was placed in prison due to fraud allegations considered by some to be politically motivated [source] ) or constant ballot registration rejections and this happens always/most of the time then you can expect that it happens due to fear.

Boris Nemtsov used to be one of the most important political figures before he was assassinated (this site states that opinion polls in 1997 say that Nemtsov had a 50% chance of winning the 2000 presidential elections). He once held the post of deputy prime minister of Russia before being assassinated in 2015 (the source here states that Nemtsov was working on a report that was potentially damaging to the Kremlin). This death would seem a bit odd considering the circumstances

Answer 2

The answer will be Yes. You don't even need to be clearly the biggest. Have some positive dynamic and you will get removed from the political landscape.

Other examples outside of western/liberal bias are DPNI (Golden Dawn-like nationalist movement, dissolved in 2011) and Rodina (AfD-like party, existing now as a hollow shell, never nominating any competitive candidates).

Eduard Limonov, a prized Russian writer and politician, has cycled through multiple successive movements as they were being outlawed.