I have some understanding of Russian mindset, having escaped it a few years back.
Russia was snipped on the nose quite badly when it came to Iraq. Not only did the advisors they had there recently and the systems they sold to defend failed, but they also now may be exposed for trading illegal items to Iraq.
So now he is trying to be as contrarian as ever, in hope that once he relents on the embargo matter, in turn the West will not press him on the illegal trading. So he is A. flexing his political muscle for the benefit of his people and the worlsd stage and B. setting up a potential negotiation tactic, and a point he can later gracefully concede in excchange for something. Perhaps some oil contracts, more likely suppression of evidence of illegal activity. USA is not going to pick a fight with Russia anyway.
Finally, he claims there are no WMD, and lifting the embargo will let people forget about that issue. He wants to embarass US due to lack of WMD so far as long as possible- also setting up for a point he will concede in exchange for something else he wants.