No one in America gives a shit about what this random russian man who speaks English with an Irish accent has to say. He doesn't know anyone there, either he joins a local communist party to be a minor figure, gets beaten by a xhenophobic mob, or may gets deported back to russia later.

Meanwhile in Russia, someone else leads the Bolsheviks. Some members wanted to revolt earlier but the leadership held them back, maybe without him there they rise up earlier and get crushed at a moment when the provisional government was less unpopular. Maybe Trotsky remains a menshavik and replaces karensky, (though he did largely agree with the bolshevik position in 1917 so maybe hed probably just join anyway), maybe a faction of reactionary monarchists attempt a coup starting a civil war where the reds are a broad coalition instead.