Only a few years ago, the idea seemed unimaginable: the United States is planning to give considerable military assistance to Armenia, Russia’s not-so-long-ago strategic partner. But times have changed, and Washington is treading cautiously as it works to erase a geopolitical red line in the Caucasus. The Armenian government started distancing itself politically and economically from Russia after experiencing a crushing defeat at the hands of the Azerbaijani military in Nagorno-Karabakh. The widespread feeling in Yerevan was that the Kremlin failed to fulfill its security commitments to Armeni…