The SRs won the large plurality of votes in the 1917 Constituent Assembly elections. They had broad appeal to many Russian peasants, workers, and the leftist intelligentsia. The Left-SRs were key to helping the Bolsheviks gaining control shortly after the October Revolution.
What would happen if the Bolsheviks were weaker prior to October, and somehow this allowed the SRs to be the greater drivers of the 1917 Revolution later in the year? and somehow managing to transition Russia towards a democratic republic, though quite left-leaning?
What would be required domestically and abroad (namely WW1)? Would the civil war be avoided if the Constituent Assembly isn't dissolved and managed to forge a left coalition that had a majority of its seats?
Who lead this Russian republic (Chernov? Kerensky? Both?)? Would it become federal with lots of granting of autonomy to the various nationalities (Ukraine, Central Asia, Idel-Ural, Caucasus, etc) and managing to have the extend of OTL USSR, and how would the economy run (the NEP, essentially state capitalism but with the SR promise of land socialization)?
Implications for beyond the 1920s? How would this impact European politics and relations?