Stalin should have openly supported the CNT/FAI as well as the Republican government
I guess Stalin should've deployed Soviet armor and airforces to help fight Spanish fascism, maybe even send Soviet armaments and training cadres.
Wait no he actually did that.
The actual blame, yet again, rests on France and England chosing "neutrality" while the Italian and German fascists were running hog wild in Spain before Soviet intervention.
There can be arguments made that there could've been more done by the Soviets, if we ignore historical conditions that the Soviets faced a very real possibility of a two-front war against the Japanese imperialists in Asia and the German-Italian fascists in Europe thus having to prepare for such events, yet insofar as I've seen the Soviets did the best they could in the limited capacity that they could afford.