If Hillary Clinton didn't have such high unfavorables it wouldn't have been a contest. If Bernie hadn't siphoned off some of her support it wouldn't have been a contest. Russian meddling and Comey's last-minute maneuver definitely cost her the election, but only by swinging the vote less than 1% in a few key states.
I don't think Putin seriously believes he can control US elections and probably recognizes this as a one-off lucky break.
The whole point for him is the PR value: having Trump claim elections are rigged is pure PR gold for Putin. Having Trump claim protesters are paid Democratic shills (rather than real people who don't like him) is Putin cover. He gets to point at those words and say "see, it's the same everywhere". It gives Putin supporters cover to believe his lies and it takes the wind out of the sails of Putin's detractors.
My guess is Putin's original plan was to take advantage of Trump claiming he lost due to election rigging but we'll probably never know.
