I don't know enough about that to be sure why Russia is considered our enemy---and neither does anyone else who has time to post here.  I do agree in general that it's usually a good idea to get along with whomever you deal with (friends, enemies, business associates, spouses, neighbors), but that's not my call regarding Russian relations.

I know that in big important organizations like Congress, the Justice Department, the White House, etc., there's a lot of top secret information you and I can only speculate on.  Within these organizations, transparent communication is essential to keeping things running smoothly and nobody going rogue with their own self-serving agenda.

When Flynn and Sessions LIED about their contact with Russian personnel, that untruth alone compromised whatever system is in place.  Agree?

Then you could add in whatever secret communications that were so huge they HAD to lie about it.  Do you have a theory as to what was discussed and why they lied about it?