There is another limit to US power, in a large, prolonged, but conventional weapons only conflict.
(If this would ever be possible in the case of Russia).
I've alluded to the strains the deployment of large scale forces to Iraq, over 5 years, has created.
(And there were nowhere near enough boots on the ground just after the invasion and for years afterwards, a factor in the entry of outside terrorists and the domestic anti Western groups).
Something bigger than Iraq, that went on for a long period, would need some sort of Draft to be re-introduced.
That is pure political poison in domestic US politics.
Given that the territorial integrity of the Continental US is not going to be under threat from an enemy army.
Now the size, range, reach, technology available to the US, makes that sort of situation unlikely.
'Silver Bullet' technology like stealth, the Carrier Battle Groups, command and control networks, satellites for spying and communications, the reach of what used to be Strategic Air Command assets.
But, consider how Cheney, in the quote posted in the thread above, was largely responsible for a complete about face on Iraq less than a decade after that quote.
So never say never.
Russia, does not have that problem, there was wide public disenchantment as the 1980's Afghan War rumbled on, not that any ballot box could change that in the Soviet Union.
But that was also about the crumbling economic conditions in the USSR
Military service, though not popular and often brutal, is embedded into the national psyche.
We have seen how wide public disenchantment over Iraq, did in time embed itself with the US public, a public used to short, sharp conflicts over the previous 15 years.
The US public today, though generally more patriotic, in the sense of supporting their military, than many of it's NATO allies, this is in the contest of an all volunteer military.
Though it's hard to envisage a full scale, extended slug-fest with Russia, or anyone else, who knows what lies around the corner?