He would have instantly been viewed favorably on this issue and likely wouldn’t have tanked his polling.
His polling didn’t tank in tandem with the Gaza genocide.
Most Americans are either in support or ambivalent towards Israel in this conflict.
Every poll I’ve seen asks the most important issue to voters, and it’s always the economy, with the Israel-Palestine conflict coming in near the bottom.
Israel is committing a genocide, to be clear. The moral thing is to, at minimum, stop supporting their genocide. But that’s not the same as saying that the Palestinian genocide is what brought Biden’s poll numbers down, or that it’s a silver bullet (or even an unambiguous net gain) electorally speaking.