It's the nationalistic sentiment of Russian people.
Whenever Putin is inventing some new issues and posing those issues to the Russian nation, they are becoming united and are worshipping Putin as a "Great Leader." Sometimes, Russian national issues are not invented by Putin though. They come naturally, but the beneficiary is still Putin.
If you look closely, the graph reached, for instance, at its peak in June 2015. Do you remember what happened during that period of time? Well, that was when Russia intensified its war in Eastern Ukraine.
You will see another spike at the end of 2015. Do you remember what happened then? Well, that was the time when Turkey shot down a Russian military jet.
Any time there is a stunt, that is instantly propagated among the general populace and Putin gathers more support.
- Syrian intervention
- Hypersonic missile claim
all are Putin's inventions to gather more support and rating.
If I remember correctly, Putin's 2012 election was a very tough win for him. Can you guess why? Well, that election was held in March 2012, and he could not invent anything new from the end of 2011 to March 2012. So, he hasn't made the same mistake this time around in 2018.
Now, the obvious question is, why does Putin need to invent those things times and again?
Well, you have to remember that Putin's rule is fraught with authoritarianism and extreme corruption. Russia isn't progressing like the West as what most of the people expected during 2008. Besides, Putin regularly blocked opposition leaders (real opposition) from taking the streets and gathering mass supports. So, there you have your answer.