No, it isn't.
These are the rantings of a paranoid, crazy person (Putin), it's simply an excuse to do evil, how would America even be a big threat to Russia? Do we actually believe America would invade Russia unprovoked or something? If America wanted to attack Russia, they would have done so already but nobody wants a war with a nuclear capable country, that is exactly why the world isn't aiding Ukraine militarily right now.
I will repeat that Ukraine is a sovereign country and has the right to decide its own future, Putin isn't protecting Russia from anything, he is acting like Hitler, the only 'threat' of Ukraine joining NATO is that Russia can no longer invade it.
Also, NATO is a lot more than just America.
Maybe no to you, but yes to us. We - Vietnamese - know how dangerous US are since their invasion in the past.
And Nato was created to deal with Russia and their allies.