Its possible for a nation to overestimate their military might. Look at some of the US's embarrassing wars when they were forced into Guerrilla warfare. But there are still limits. There is no way russia thinks they can beat Nato in a conventional war. Its why their strategy is around developing technologies that maintain nuclear effectiveness (though I think anyone looking at the numbers has to have some serious doubt about how nuclear capable russia really is).
Yeah, at this point Russia wouldn't even stand against Europe, let alone America's toy box of death. The only thing keeping everyone is the danger of nukes, because that's somebody nobody wants to risk even if we have meassures. You never know what could happen. But a conventional war? nah.
Because this is like the biggest strongest kid in school and all of their 6ft + tall 250 pound friends handing out sticks to the bully's victim so they can hit back and the 5 ft nothing 150 pound bully decides "you know what? Id like to fight these people directly while im bullying this other kid"
Because there would be no Russia left. They have issues with 80s and 90s tech in Ukraine. Imagine if they had yo go against the new shit. Oh yeah also NATO is a thing and European Texas (Poland) is next to them, not to mention Germany finland, and France.
They also are quite afraid of where China will stand on that.
Because it would be suicide. Russia is fond of saber rattling and "oh-so-serious" threats about nukes, but Article 5 means they're never attacking a NATO power. They don't actually want to escalate either (I assume - it'd be catastrophically, titanically idiotic) but like a very, very small dog, have to yap loudly so nobody notices.
And over military aid? Nah. Best they can do is "punish" it by keeping sulking and whining hypocritically, same as they have been all along.
Before they attacked Ukraine the second time, Russia had a GDP smaller than the state of Texas by itself. Texas isn't even the largest state GDP in the USA. The US military budget is 3/4ths of the entire Russian GDP. There is no contest. Russia is a bad joke.
Because of alliances. We have them and Russia doesn’t. Our military is massive and strong but it won’t work if nobody lets you inside their borders or sea and airspace.
Russia is already a paper tiger in Ukraine, them declaring war on the US would result in an 8-12 month war, that replaces Putin with warlords, and after that Putin's image would be way worse than of Stalin's and the last Tzar's combined.
Strange you think the war would last that long. In reality, day 1 of the US's attack would involve wiping out all of Russia's air defenses and preventing so much as a dji drone from taking off. After that they just land a team in Putin's office and slap the man in the face.
Russia can't even beat Ukraine with their surplus second rate western weapons. NATO, because that's who the fight would be against, would destroy Russia. If Russia used nukes everyone would die. It's a loss for Russia either way. No one outside of Russia believes that Russia even had a hint of a chance against NATO. The Ukraine war has made that very clear.
Because their weapons are no match and they can't sustain prolong war that the US can afford. The only way they could possibly win is through nuclear arsenal. Their strategists are not fool to commit that. Almost suicidal.
Politics. They don't went to be seen as the aggressors.
Remember the who Ukraine thing is to liberate Russian speaking people from living under (what they call) an oppressive regime. Declaring war on the US will also be a declaration of war against nato, as one of the NATO agreements says a war one one member is a war on the entire NATO block.
Money. Many wealthy people in Russia stash their money overseas, most sanctions for the Ukraine debarkle are only going after a few at the top. If a declaration of war happens, it gives the US power to go after more of their international money and investigate anyone receiving money from said government meaning they loose political influence over the west.