Reisner advocated for replacing the Polizeistaat model, which he considered outdated, with a "cultural rule-of-law state" that would guarantee the rights of the Empire's citizens, including freedom of conscience and religion.
At the end of 1905 Reisner returned to Russia and participated in the organisation of the First Conference of the Russian Social Democratic Labour Party in Tammerfors.
After the defeat of the 1905 revolution, because of his Marxist views, he had to emigrate to Germany and France again and subsequently lectured at the Russian Higher School of Social Sciences in Paris.
After the October Revolution of 1917, he was appointed a professor at the University of Petrograd, where he helped to develop the first Soviet constitution.
His daughter Larisa had died two years earlier, while his adoptive son Lev perished in a camp in 1941 but was later rehabilitated under Khrushchev.