None dare call it treason.
Exclusive: Trump campaign had at least 18 undisclosed contacts with Russians
At the least, they collaborated with Putin in an effort to make American policy less adversarial toward Russia, the Buchananite/Bannonite agenda.
A less charitable but also objectively accurate construction is that they acted in conscious collaboration with an inimical foreign power in undermining American national security to the particular advantage of that same inimical foreign power.
All that quite apart from any proof of express collaboration with or guilty knowledge of Russian efforts to manipulate the election in Trump's favor.
Some day, someone will write a book about the 2016 campaign with a title something like, "Donald Trump. How an Ally of a Russian President won the White House and set out to undermine American National Security to his advantage."