Serious Marxists of the past were very clear that participating in electoral politics is at least sometimes constructive, but that's not the same as electoralism (a plan predicating on victory through the primary means of winning elections) or entryism (trying to have electoral success within a rightist party to steer it toward socialism somehow). Supporting DSA dems who are already campaigning is whatever, I guess, if they have good policies, but the best thing to do is actually have your own platform that you have full authority over so that you can spread a message of undiluted socialism (rather than play PR games like Mamdani) and force reactionaries to contend with it.