This is very suggestive. The White House is claiming that this is it, but we know that it is rare for there to be a “lone wolf” in American politics.  Go back to Iran Contra. Thus, this builds toward Trump, but it is still only suggestive. If the transition team was smart, they would have protected Trump. Like Iran Contra. So it may not reach as high as the president. Obviously, the administration will argue that this is it, that Flynn was on his own and that it does not implicate the president; but opponents will maintain that this is one piece of a puzzle that will implicate the president. Only time will tell who else is talking, and whether this reaches the president.  The big question is WHY would Flynn have lied?

American should expect some additional insight into the Russian investigation in the near term, but the slow drip of the investigation will continue after this. There are larger concerns about what this means for American government and the presidency.  On the one hand, it is a potential disaster for the current administration if more evidence of, shall we say, a problematic relationship with Russia continues to develop.  On the other hand, the investigation shows that our institutions are performing properly and just as they are slow to resolve complicated issues, they provide an important check on abuse of power.

Politically, this is more of the same.  The Administration’s supporters will not be swayed by this guilty plea and opponents will remain convinced that Trump colluded with Russian.  It will take something more substantive to move the needle on Trump’s support and, like with Watergate, it will begin will key senior legislators of his own political party.

On whether this is a violation of the Logan Act:

One could be in violation of it if one negotiates with another nation, particularly a nation that the US has questionable relations with (like Russia), in an unauthorized position. It’s all theoretical and any enforcement of the Act would be at the discretion of a prosecutor, and so we’d have to look to Mueller to see if he would do this.  For all we know, this could have been floated as part of the plea deal. Certainly the Trump Administration would argue that Flynn was “negotiating” (if he was) as an incoming White House official, and so it would have been authorized.  But that would only apply to end of 2016 and beginning of 2017.  Hard to know at this point what Mueller found regarding previous contacts with Russia.