1). The popularity of a Russian leader, historically speaking, increases proportionately in relation to how much that leader is disliked or criticized by the international community. Their popularity increases the most when their country is at war or invaded.
2). Said Russian leader assassinated very publicly a former Russian spy in the UK using a nerve agent that intelligence services in Britain would certainly trace back to the Kremlin. Putin wants everyone to know it was him who ordered the attack.
(Putin has publicly killed his enemies for the sake of consolidating his domestic strength on three occasions, e.g. the most recent attack in the UK, the use of Polonium against Litvinenko, and the shooting of Boris Nemstov (an outspoken Putin critic) on the steps of the Kremlin. The numbers go up considerably when we include all of the journalists he’s killing in his country.)
3). International community predictably plays its part in the narrative by reacting with outrage. Russian citizens circle their wagons around the puppet master and defend Putin.
4). Putin wins election in two days by landslide as the populist leader and defender of the mother country.
5). Democracy in Russia continues not to exist for at least another 4-5 years. Minorities in that country continue to suffer and we get to continue on with the Cold War 2.0 and a suicidal arms race preparing for a third world war no one can actually win.