This is now two sources - the AP and David Ignatius - confirming the fact that Michael Flynn was in contact with the Russian Ambassador multiple times on the day Obama expelled 35 Russian diplomats as punishment for hacking. The dossier outlines several Trump staff in regular contact with the Kremlin and plotting hacks against Americans and American organizations. It also references Russian diplomats in the United States.
Imagine your shock if you're Flynn, and you've been engaging in some treasonous activity with a Russian diplomat, and the POTUS expels that person from the U.S.
The uncertain relationship between Trump and the Russians is a security risk that could lead to impeachment. Trump may have overstepped his boundaries in order to gain the presidential election. If a Trump aide was found to be using Russian influence to impact the election, it may be a turning point for impeachment.
No, Donald Trump's frequent contact with a Russian envoy will not get him impeached. The only people who have any guts in Congress are the Republicans. Democrats are a bunch of cowards who just want to play nice. As long as Trump wants to make the rich richer at the expense of the middle class, Republicans will not try to impeach him.
No, the fact that a Trump aide was reportedly in frequent contact with a Russian envoy will not likely cause him to be impeached. The aide was the one in contact with the Russian envoy, not Trump himself. It would be difficult to link the President-elect with the actions. It's another time when he has walked the line and come out ahead.