I highly doubt that, since his administration was actively financing anti-Assad groups, including violent religious extremists. We've been fighting a proxy war

I highly doubt that, since his administration was actively financing anti-Assad groups, including violent religious extremists. We've been fighting a proxy war with Russia in the Middle East for roughly seventy years and Syria has been Russia's #1 ally in the region for decades. He'd have to have his head in the sand to think that Russia would allow him to directly take out Assad's forces. He made a horrible decision that reeks of hubris, thinking that nobody would call his bluff.