cast lot with

cast (one's) lot with (someone or something)

To join and steadfastly support another person or group. As soon as news of the CEO's scandal becomes public, I doubt that big investor will want to cast her lot with us. Don't worry, Mom—I really don't care about casting my lot with the cool kids at school.
See also: cast, lot
Farlex Dictionary of Idioms.

cast (one's) lot with

To join or side with for better or worse.
See also: cast, lot
American Heritage® Dictionary of the English Language, Fifth Edition.
See also:
  • cast (one's) lot with (someone or something)
  • cast one's lot with
  • throw in (one's) lot with (someone or something)
  • throw in your lot with
  • throw in your lot with somebody
  • throw in your lot with someone
  • to a person
  • blow (something) wide open
  • blow something wide open
  • blow wide open