Assuming Russia does become a "democracy" in the 1800's, it'd still retain an elitist culture.
The "liberation" of the peasants in 1861 only served to postpone the peasants' yearning for the landowners' land.
A Russia that went through a longer period of reforms would still retain elements of feudalism, and all of the drawbacks to boot.
As for the nascent working-class centered around the cities, they wouldn't be much better off either. Radicals would still be able to find an audience in the factories.
As for the United States having a communist revolution, Stalinist-rule is out of the question.
Stalin and the style of rule named after him was a strictly Russian affair-and even then it was only the result of civil war.
The Bolshevik Party following the 1905 Russian Revolution, and the October Revolution of 1917, had become temporarily more liberal. After 1905, the central committee's powers were scaled back, and Lenin pondered over the spontaneous power of the proletariat and it's relation to the party, which he originally dismissed in What Is To Be Done? as "bowing to spontaneity."
It wasn't until 1918, when the threat of full-scale civil war loomed, that the Bolshevik Party and the government that it led both became centralized. Factionalism-chiefly encouraged inside the party-was banned in 1919 in the interest of party unity.
Another killer to the nascent national democracy inside the Russian revolution was the dissolution of grassroots-democracy. With Bolshevik and Left-SR cadre sent off to the front, and more and more bureaucratic positions being needed to run the crisis-ridden government, many bottom-up organizations responsible for the popularity of the Bolsheviks amongst lower-class societal members...simply stopped their work in the interest of "saving the revolution," IE through centralization. With them, agitation and propaganda amongst the soviets, key to the Bolshevik's success before October, halted too.
Keeping this in mind, there would no doubt be a civil war in America, between two classes: the proletariat and the bourgeoisie.
The U.S. constitution, at it's very heart, upholds private property. communists historically have sought to create a common property, with which to eliminate the inequality associated with private property.
For the right to either keep the old constitution, or write a new constitution, a civil war would be waged.
Because national conditions were no doubt different in the U.S., a strong working-class squaring off against a stronger bourgeoisie, it would remain to be seen who'd take up a vanguard role in the national revolution.
What would be interesting to see is a syndicalist U.S., but of the genuine type-workers' councils, grassroots trade unionism, etc.
It would be more interesting no doubt then the U.S.S.A.!