Kamkov was also involved in organising aid to Russian prisoners of war, using the opportunity to distribute revolutionary propaganda.

He became a leader of the staunch anti-war faction of the PSR, along with the Maria Spiridonova, Isaac Steinberg, the veteran Mark Natanson and others.

This put him in opposition to the Revolutionary Defencist SR and Menshevik leaders who dominated the soviets during Kerensky's government.

[note 1] Kamkov occupied various minor posts in the PSR but increasingly called for a break with the Defencists.

Kamkov favoured some agreements between all socialist parties, a popular position at the time, feeling that "the Left should not isolate itself from the moderate democratic forces.

The 'Left Communists' were eventually brought to heel, but in March 1918, the Left SRs resigned from the Soviet government in protest against the peace treaty.

Kamkov was involved in many of the activities of the Left SRs over the next few months: organising resistance to the Brest-Litovsk Treaty and to the Bolshevik policy of forced grain requisitions, holding merger talks with the 'Socialist Maximalists' and Ukrainian revolutionary groups.

In June 1918, the Left SRs abandoned the policy of peaceful protest and began to organise illegal strikes, uprisings and assassination attempts.

Mark Natanson was one of the most prominent Left SRs, but alone in his desire to call for continued co-operation with the Soviet government.

On July 7, Kamkov helped organise an armed anti-Bolshevik demonstration by Left SRs, which was quickly suppressed.

In 1937 Kamkov was re-arrested, with the intention of using him as a witness in the upcoming show trial of Nikolai Bukharin in March 1938.

However, Kamkov steadfastly refused to incriminate Bukharin in the charge of having plotted with the Left SRs to assassinate Lenin back in 1918, in spite of severe pressure from the GPU.