According to the leaks, a senior member of the incoming Trump administration had discussions with Russian diplomats concerning a matter of US foreign policy. That, in fact, is desirable in situations like this. In this case an outgoing president acted rashly against a foreign country in the final days of his administration. If the incoming admin doesn't agree with that act, they should indeed let the other country know that everything's going to be OK in a week or two. Why have the other country retaliate against America, when it can be avoided?

Any legal liability for having contact with Russian officials could be easily skirted by offering a disclaimer: "I'm not discussing official US foreign policy here. I'm just hypothesizing that if you don't retaliate against Obama' kicking out Russian diplomats, it might work in everyone's interest. Etc."