Why are Russians so bothered by Mike Flynn's departure?

There are two facts about the Michael Flynn saga that stick out at me today:

1. According to The Washington Post, Flynn had contact with Russian ambassador Sergey Kislyak not just during the transition - a time when Flynn can plausibly argue that conversations about policy were appropriate in preparation for taking office - but during the presidential campaign. The Post cites both "officials with access to intelligence reports on the matter" and Kislyak himself as confirming that Flynn and Kislyak were in contact before November 8.
2. According to various outlets, including The New York Times and CNN, Russian officials seem quite distressed about Flynn's departure. Press secretary Sean Spicer insisted Tuesday that Trump's administration had been "incredibly tough on Russia." Yet there seems to be a sense in Russia that there is room for American policy to get tougher with the departure of Flynn - a man who followed up his dismissal from the Obama administration by giving a paid speech in Moscow for Russia Today, the Russian government's English-language propaganda network.

So, what were Flynn and the Russians talking about before Trump was elected - during a time when American intelligence agencies believe Russia was trying to influence the outcome of the election in Trump's favor?

And why do the Russians seem so concerned that Flynn's departure will be detrimental to their interests?

These will be interesting questions to explore if Flynn is subpoenaed to testify before the Senate Intelligence Committee, as several Republican senators seem eager to see happen.

This is an opinion column. The thoughts expressed are those of the author.