Dude, Russos posses a huge stockpile of sophisticated WMDs, they do have a sophisticated air defense than the world combined, they do have a couple of unknown weapons that can be a surprise to US.
It is really hard to tell what will happen if they choose to fight (very unlikely though). Problem is they do not have money, and hey do not have strong allies.
It is probably the only nation with really capability of blinding US and shooting down its birds with multiple stone launchers like Tor-m1 and S-400