Slonim was present in the Assembly on the morning of January 19, 1918, when the Bolsheviks dissolved it by force and opened fire on the supporting crowds. For a while, he was in the Ukrainian State, helping Gregory Zilboorg put out a clandestine paper which angered both the Bolsheviks and the Ukrainian nationalists. He later fled to Samara, where the Constituent Assembly had formed its own "Committee of Members" government. He joined the latter, then, upon its merger into the Provisional All-Russian Government, moved to Omsk. As the Russian Civil War took hold of the countryside, Slonim followed the Czechoslovak Legion and became friends with its leaders, trailing across Siberia under an assumed name. Nevertheless, he disliked the concept of Allied intervention, and moved closer to the Left Esers. His party sent him abroad as a member of its Foreign Delegation, which originally existed to put persuade the West not to recognize Alexander Kolchak as Russia's Supreme Ruler.