Wow. Conservative Garner, who bitterly fought against 2nd New Deal and fascist sympatiser Kennedy vs. liberal Republican and New Dealer La Guardia and Progressive La Follette? I'd definitively vote Republican ticket this time.
Without FDR endorsments, Garner would be in HUGE trouble. Most of New Dealers would fly to La Guardia. And FDR himself would secretly back much more ideologically close NYC Mayor.
BTW, Did you know that Roosevelt personally said, he could accept La Follette as his potential successor? During the war he would probably abandon isolationism as well.
Witch such ticket winning and history course change we could have Barack Obama (R-IL) vs. John McCain (D-AZ) in 2008