WASHINGTON — Morris Katz, the Gen Z political guru behind the rise of New York City Mayor Zohran Mamdani and Maine Democratic Senate candidate Graham Platner, has offered a groveling, belated mea culpa over the latter’s campaign implosion after he was accused of rape. But one former ally isn’t buying it, branding him a “twerp from Tribeca” — and suggesting there’s more dirt to emerge about Katz’s failure to vet Platner before backing him to run against Republican Sen. Susan Collins. In an interview on “The Ezra Klein Show” released Friday, Katz — a co-founder of lefty consulting group The Fight Agency — acknowledged the campaign’s lapses in judgment. But, he claimed,...