Lieutenant General Micheal Flynn was one of the closest advisors on security to Donald Trump. He had the ear of the President and obviously whatever he did could only be at the behest of Donald. Now we have a case where Flynn has either been asked to resign by Donald or he quit on his own. This is immaterial as the main fact that a close advisor and supporter of Donald has to go for something which he did maybe at the behest of Donald,\
Flynn is accused of discussing sanctions imposed by Obama with the Russian ambassador. The Americans consider this a breach of security, though just how talking to the Russian ambassador compromises Flynn beats one's imagination. The American politicians are paranoid about Russia and hence Flynn had to go.
The entire episode weakens Donald as Flynn was in reality just articulating the approach of Donald. the knives will soon be out for Donald and he better watch out.