Those boring leaks probably came from the inside.
Especially because Trump was objectively pretty anti-Russia, and did a lot of things that pissed off Russia. But there is too much hysteria around "OMG RUSSIA AND TRUMP" and general FUD propaganda for anyone to see the forest for the trees of "orange man bad"
Believing Putin over his own intel agencies -- and publicly proclaiming as much -- is actively pro-Russia.
If Trump didn't want people to think he was a Russian asset, he might have tried not acting like one.
Their main objectives for the 2016 election was to prevent Clinton from being elected and to maximize internal division in the US; Trump was the main recipient of their support, but they also used their influence operations to support candidates to Clinton’s left (with varying responses from the candidates themselves) including Sanders (who publicly addressed it after being briefed on it, telling Russia to get out of US elections).
> How did that ever make sense?
Weakening NATO and Western unity alone was a pretty good benefit; its hardly the only place in the West where Russia, around the same time, backed nationalist political movements to disrupt internal or international unity in the West.