DSA as in Democratic Socialists of America, politicians like Mamdani.
Personally, I don't think Democrats are worried about the DSA in the slightest because DSA candidates run on the DNC ticket.
They quote Schale, a "strategist" working for the DNC, who thinks that the DSA has an unrealistic platform which distracts from the DNC platform.
It just doesn't make any sense to me. "Oh no! Passionate and popular candidates are running for our party and winning over people who generally don't vote for us! We might even win back a true senate majority, soon!"
Like, if it were me I'd be cool with it no matter how much Mamdani might give me the heebie jeebies by shaking hands with Trump and pissing off certain large donors. (this is a hypothetical, I actually hate those donors)