I'm not disputing that a few such people exist. But they probably number in the tens of thousands, in a country of hundreds of millions. You are acting like the people living in tents and taking over buildings on Columbia's campus are somehow the "rank and file" of the Democratic Party. It's laughable. There is no real country-wide "problem" with pro-Palestinian radicals, unless you happened to be a college administrator last year. You are simply being manipulated by right-wing media into believing that fringe issues are the most important things our country is dealing with. Just like you thinking that a Sydney Sweeney jeans ad is some great cultural revolution because Fox News et al. won't shut up about it.
But in any event, your fixation on Mamdani (who got something like 40% of the primary vote in a city-wide election) is an avatar of the Democratic Party as a whole is silly. Do you like in NYC? No? So why do you care so much about what a mayoral candidate will or won't denounce when it comes to foreign policy? Meanwhile, Trump won't denounce J6; Trump won't denounce the Proud Boys; Trump won't denounce Putin and the other dictators he sidles up to constantly, etc. These are the things you should concern yourself with, not trying to parse what a few college kids and one mayoral candidate say about Palestine.