He won with less than 3% of the vote where he faced claims of vote-rigging claims from coincidentally the Luhansk, Crimea and Donetsk regions where people were double-voting, it's not a coincidence where the only regions he won are now currently in separatist control, more importantly the very first thing he did in office was withdraw the Constitution of Ukraine which was first made in 2004 which involved closer ties to the EU and joining NATO.
And the fact he was impeached with a vote of 328-0 suggests the penny dropped the man was a double-agent.
He sold himself out for Russian protection to try and stop the navigation towards Europe but what Putin simply cannot accept is that it's the people's wishes for a sovereign country to be part of NATO, the country is overwhelmingly in favour of part of the West rather than a ex-USSR state, the only ones that aren't are now the ones who now have Russian passports and are now part of unrecognised republic.
Putin's aim is not to fly the Russian flag in Kyiv, it's just to simply put another yes man in charge to withdraw the constitution again, as evidenced by what's been on the news where the British Government have put sanctions on Ukraine's own MP's who were willing to be the next yes man.
The main problem Putin has is the sheer size of the country which means Kyiv isn't the only major city who is pro-EU, if Kyiv ever fell then Kharkiv would probably end up as the de-facto capital where the Nationalists would base themselves and fight the separatists leading to another Syria which will go on for years without a conclusion.