I don’t have the exact quote, but Lenin did say to judge a party not by its slogans and names but by its actions.
“In order to understand the real significance of parties one must examine, not their labels, but their class character and the historical conditions of each separate country.”
—- Lenin, “The Labor Government in Australia”
Nope, he used to be active in the World Workers Party, but he left years ago. He pushes for going “out of the movement, into the masses”, being generally dissatisfied with all the US socialist parties and views the movement as having been going nowhere. So nope, he’s not in a ML party right now and it doesn’t seem like he’s going to be either.