They've never been our ally in any meaningful way. They used nuclear blackmail against Nixon to bail themselves out when they lost the Yom Kippur war. They blew up the USS Liberty and machine gunned my great uncle in the water. And they were literally the reason for 9/11, straight from the mouth of bin laden.
The people in general don't, but corrupt politicians rely on AIPAC and other foreign influence pressure groups like it for both bribes and free demonization of any anti-genocide opponents they may encounter.
I love the implication that in an alternate universe, where the US is allied with Germany for some reason, the response to the holocaust would be unconditional support.