First of all, this isn't a question about invasion. OP asked why Russia and US can't be allies, and the GP said one of the reasons is because Russia is not a democracy. US has shown time and time again that democracy only matters when it suits them. US is an ally of Saudi and a lot of monarchies in Middle East; Saudi, Qatar, UAE and Kuwait. US also overthrew a democratically elected govt. in Iran for a "friendlier" Shah. You also have Operation Candor.
So to sum it up, my point is, when it comes forming alliances, US is willing to overlook democracy. I don't know why you're bringing up invasion.
Also, as an aside, if a country is not democratic, that doesn't give US right to invade it and you don't get to justify it.
Your point is unclear. You named just a few non-democratic US allies. There are hundreds of countries on the planet and pretty much all democratic ones are US allies. So it is clear that being democratic is a strong major factor. And exceptions just show that there are other factors though seemingly less important, and that the democracy is not a 100% requirement.
> if a country is not democratic, that doesn't give US right to invade it and you don't get to justify it
You made up something here, that nobody disputes, attributed to an unnamed set of opponents, and denied it. This is messed up. You should not be doing that in a reasonable discussion.
That was literally my point. GP said one reason Russia and US might not be allies is because of democracy, when clearly that hasn't stopped US from being allies before.
So to sum it up, my point is, when it comes forming alliances, US is willing to overlook democracy. I don't know why you're bringing up invasion.
Also, as an aside, if a country is not democratic, that doesn't give US right to invade it and you don't get to justify it.