Well you could have Edouard Vaillant winning his "war" with Jaurés and the rest . But Guesde was pretty much a men of the past in the french left at that time, he was already there during the Commune of Paris so he was very much a radical thus without a hope to assemble the left .
So it's kinda hard with a After 1900 . The radical having been either purged, send to Guyana or New-Caledonia or sidelined b the event of La Commune (or even their afterward support of it )
Is it possible to have a less violent suppression of the Paris Commune so that the radical elements aren't killed or exiled? That way they could continue to influence French politics. AFAIK this POD won't cause any major butterflies in Marxism, which in turn means no major butterflies in the Russian Civil War