Today he also said he was in support of AES

After Stevens' open defection he had no choice. If he doesn't, he gets outed too, because he supported her so strongly in the primary.

Or to put it another way, she put a shiv in El-Sayed's back, sure, but it could be argued that it was a much bigger shiv in Schumer's back.

El-Sayed is surrounded by enemies of all kinds who are united in keeping the status quo unchanged. Schumer is not, and willingly brought the weight and power of his own position to help Stevens.

In the end Stevens is just more water off the back of El-Sayed, who is making his own way regardless of all those coming at him, always has, and he was not thrown off his own course in the slightest. On the other hand, Schumer is struggling in a number of ways.

So it begs the question: who bears the greater betrayal? It would have been very odd if Schumer had not vocally supported El-Sayed today. He may well need that favor back in days to come.