First, its meaning is compositional, or rather, follows the meaning of the indiviudal words it's composed of. So, it's not an idiomatic expression.
Second, the idea it expresses is not trite. It houses important meaning.
Third, it's a phrasal verb:
To aid the cause of by approving or favoring.
Synonyms: advocate, back, champion, endorse, get behind, plump for, recommend, side with, stand by, support, uphold.
Idioms: align oneself with, go to bat for, take the part of.