It had everyfucking thing to do with it. Are you really that ignorant of history? It was a test of the political and military will of the fascist movement sweeping Europe. Without fascist success in Spain and without being able to test blitzkrieg philosophy in actual combat there is a real chance delays Polish invasion or German Army gets bogged down by logistics as it almost did anyway in Poland.
You really need to learn fucking history.
The left was stridently anti-fascist and on the front lines of raising the alarm to fascist expansion. As far as prominent anti-fascist on the left, FDR, Harold Ickes, George Marshall, Ben Cohen and Thomas Corcoran. All left new dealers. All stridently anti-fascist and all working against German fascism before we went to war. Ben Cohen and Thomas Corcoran authored the Lend Lease legislation to aid Britain. You really to study history and not the bullshit lies that right wing propaganda sites put out.