Did you know that a President of the USA can get arrested? Yes it's true.
It is far simpler to arrest a president than to impeach them, formally speaking.
For impeachment on malfeasance in office the congress is required, for impeachment, but, if the President of the USA punches a guy in the face, on camera, he can be arrested, on site, by one policeman. What would follow would be a constitutional catastrophe, but still, Donald Trump could be arrested and charged if he engages in financial fraud. Fact. And I don't think his hubris will allow him to avoid it if he hasn't already committed it.
Likewise, if the CIA or FBI were to find collusion between Trump and Russia on illegal internet hacking for any reason, election influence aside, he could be charged with that crime, just like any citizen.
This is how Nixon was impeached. Despite selfish partisanship, Democrats are on the same side as Republicans as they get paid on the federal tax roll. They don't go around impeaching each other out of office, but with Nixon they did. And the reason Nixon was impeached is that Law authorities told congress that they were going to charge him with basic crimes, like burglary. Hacking is the same as Burglary.