Russia has recently announced they're expelling 755 American diplomats as a response to Obama's equivalent move last year:
Russian President Vladimir Putin said Sunday that the United States will have to cut its diplomatic staff in Russia by 755 by Sept. 1 in response to expanded U.S. sanctions.
Before he left office, President Obama ordered the seizure of two Russian diplomatic compounds and expelled 35 diplomats in response to the election interference, which Russia has denied. Putin did not retaliate at the time in hopes that Trump would roll back the sanctions.
But what could possibly make Putin believe that Trump is supposed to be more friendly towards Russia? Republicans in general have had a worse attitude towards the Russians over the past decades and it was actually Hillary Clinton who has started the famous "peregruzka" program back in 2009 in an attempt to improve relations with Russia.