I don't think Lang will have problems winning the elections.
He is still the leader of a victorious Germany, and this time it didn't take the ruinous price in men and the virtual destruction of Germany's economy to achieve it. Also, he's not known to be as bombastic, imperialistic and hawkish as, say Winston Churchill, so he's still the man who led Germany to victory over the murderous Soviets, who made it easy ITTL to show them as an unequivocal 'evil' enemy. Assassinations, attacking neighboring countries, attacking Germany itself, engineering the Ukrainian famine, political purges, etc. Hell, if they would have conducted Holocaust-like ethnic purges, they would basically achieve some kind of Villainous Bingo.
He just needs to remind people of that. Newsreels with "Why we fight", newspapers showing communist atrocities, also underlining the Russians as victims of a murderous regime, the movie with the murder of last the Romanovs, easing up on rationing, etc. Also, when the Soviet War troops return home, a Sieg Tag (Victory Day) for the populace, parades, speeches about how great and wonderful our boys were, etc. I don't see real problems for him to get reelected.
The Far Left and the Far Right are still discredited (for real or imaginary connections with Moscow, and enacting a Putsch during wartime respectively), so only other centre candidates will be viable, and few, if any, can show a CV at least half as impressive.