I agree with this from an opinion piece by Scott Martelle in the LA Times:
Michael Flynn’s resignation late Monday may have resolved a political problem for President Trump, but it doesn’t address the nagging questions about whether Trump, through his campaign, and then transition team, had improper — and potentially illegal — contacts with Russia. And they need to be answered.
Some Senate Republicans have already called for an investigation into Flynn, something that would be welcome, but is insufficient given the scope of Trump team connections with Russia. The Republican congressional leadership needs to put responsibility to country ahead of party loyalty to the president, and appoint an independent commission or special prosecutor to get to the bottom of it.
If criminal charges are proffered, they are more likely to be violations of the Espionage Act or of the Logan Act than of treason.
Honestly, I doubt that any investigation will convince people who’ve already made up their minds one way or the other. But it’s the way things are done under a rule of law.
It’s not unusual for an incoming national security adviser to speak with foreign ambassadors, and it’s not entirely clear that what Mr. Flynn said to Russian envoy Sergey Kislyak in late December was improper. But Mr. Flynn clearly misled The Post, Vice President Pence and other senior officials when he said he did not discuss U.S. sanctions against Russia with Mr. Kislyak. He did so in the context of as-yet- unresolved questions about Russia’s interference in the presidential election and other possible contacts between the regime of Vladimir Putin and the Trump campaign. The affair underlines the urgency of an impartial investigation into those matters by the Justice Department, Congress or an independent commission and the full disclosure of the results to the public.
Sooner rather than later would be better but I doubt that Congressional Republicans will heed that advice.