He doesn't need to do it, but the fact is that he can do it with impunity. Putin is untouchable in Russia, and so is able to crush all opposition. And as recent history has shown, other countries will do nothing to stop him. China is an ally, the US under Trump has turned its back on the world, the EU is scared.
Putin does this because he needs to scare his population into obedience. If the Russians do not heed to Putin's power, his government will fall. There is a possibility (although small) that Putin's government will not surivie due to the unpopularity of their response to the coronavirus.
Russia does not have free and fair elections, but Putin still directs Russians to vote every so often. There have been some local elections in which the opposition party has made gains.
The point is that Putin wants to scare his opposition from putting forward effective candidates, and preventing an effective from campaigning
That's literally one of the big reasons that Russia invaded Crimea.
#1. Show his people that they have military dominance over another country and ensure people in the country know their place.
#2. Show his people that he is openly disobeying the West and there is nothing that the West can do to stop him. He's trying to show that he is stronger then them.
Putin will literally be in power for his entire life. Guy isn't going to go away at some point. His leadership style in Russia has worked to maintain the oligopoly and maintain his power. Crazy shit, but that's Russia for ya.
If Biden is elected, I would expect both Taiwan and more of the Ukraine to fall to China and Russia respectively. I would also expect more of this kind of scare tactics against dissidents in both Russia and China. Both countries know they can get away with this kind of thing with a Biden administration.
Pretty sure the Chinese are a big fan of Biden due to the fact that he isn't going to be as hard on China as Trump is, or was for that matter.
Russia I'm not so sure on what their plan is. I personally don't think they care for any particular candidate though they do care about causing chaos and divide in the US. Plus Putin gets to be the strongman leader of his country which is the only reason that he still has power.
Guess we'll find out in less then a week what we're looking at, lol.