The only way the US -- read President Wilson -- would have remained neutral until the war exhausted itself (as it would have, because of the Spanish flu epidemic) was if the Russian empire remained a combatant throughout. This in spite of the occupation of Belgium, the poison gas, the submarine attacks, minefields in the Atlantic, ethnic pogroms, trench warfare, etc. The Zimmermann telegram was just a pretext.
The United States entered the war before the Russians surrendered, though. Do you mean that he would have entered the war of the Russian Provisional Government hadn't come to power in February 1917?