According to @Abingdonboy ,USAF will decimate the RUAF and wipe the floor. And looking at the Daily Beast and the Congressman's rant ,it seems otherwise. Maybe the Donald Cook Incident shook the US forces sufficiently.
S-400 will make short work of US fighters - even F-22 pilots will fear the S-400 system.
If the Russians really thought that the US may attack them, then they would have had many more SU-30s
deployed in Syria and also deployed S-400.
US simply does not have the guts to fight a country as powerful as Russia.