A Morgan Stanley analyst's downgrade of Snap was an "obituary," and the social media company is struggling in the mobile ad space like Twitter, CNBC's Jim Cramer said Tuesday. "Snap, crackle, pop," Cramer said on "Squawk on the Street." "This is (Mark) Zuckerberg going after them in a way that is only – it's not even imaginable what he is doing." Cramer...