https://www.kommersant.ru/doc/3842391
https://www.rbc.ru/newspaper/2018/12/25/5c2106f39a7947dd27cd3528
Regional experts also predicted that Russia may look to take advantage of the uncertainty created by James Mattis's resignation as President Trump's defense secretary.
https://www.newsweek.com/ukraine-russia-war-attack-christmas-1270621
https://www.gazeta.ru/politics/2018/12/24_a_12106099.shtml
https://www.gazeta.ru/politics/2018/12/24_a_12106207.shtml
https://www.kommersant.ru/doc/3841521
http://www.kasparov.ru/material.php?id=5C20BC4282C5D
https://www.gazeta.ru/army/2018/12/24/12106375.shtml
http://www.rosbalt.ru/russia/2018/12/24/1755065.html
https://www.rbc.ru/newspaper/2018/12/24/5c1d29539a794781b1a778d9