The best way to deal with the suspicions and charges that the Trump election campaign colluded with Russians is to appoint a bi-partisan commission of respected individuals to investigate.
This commission should have full authority to read secret transcripts collected by U.S. intelligence agencies and any other classified information relevant to the case, and authority to publish such information as can be done with jeopardizing sources and agents.
It should have full authority to subpoena witnesses and require testimony under penalty of perjury.
It is a federal crime for a foreign national to contribute to a candidate in a U.S. election, or for anyone to solicit or accept such a contribution. This would most definitely include the contribution of secret intelligence information.
If a Presidential candidate knowingly accept foreign help, I would say it is an impeachable offense.
The charter of the bi-partisan commission should be to determine whether there is any evidence that the Trump administration violated federal election law.
Evidence would include transcripts of communications of Russian agents and testimony by Americans regarding secret meetings of Trump operatives and Russian agents, or documents and records in the Trump campaign acknowledging Russian help, or testimony of Trump campaign operatives.
Routine contacts between Trump supporters and Russian diplomats or business people, especially if in public or in front of witnesses, would not be evidence of violation of election laws.
Even past business relationships of Trump operatives or even Trump himself with corrupt Russian oligarchs or business operations would not be such evidence—although very interesting to know.
I think it important that such an investigation be carried out by respected individuals in a bipartisan commission, and not by a special prosecutor who would consider himself or herself a failure if they didn’t find grounds to indict somebody.