the (higher order) johnson homomorphism embeds the associated graded lie algebra for the mapping class group of a once punctured surface into a certain lie algebra. calculating the image of the johnson homomorphism is a challenging problem. shigeyuki morita was the first to define obstructions to lying in the image back in the 90s. more recently enomoto and satoh have defined a new series of obstructions, and work of conant-kassabov-vogtmann has provided a rich family of obstructions, involving classical modular forms, stemming from the abelianization of the target lie algebra. in this talk, i will present joint work with martin kassabov which simultaneously generalizes all of these obstructions, making use of an apparently new action of $aut(f_n) on h^{\otimes n}$ for any cocommutative hopf algebra h.