cheerleader

noun

1. (US)A person, usually a young, attractive female, who encourages applause and cheers at a sports event, and wearing a specially-designed uniform in the official colors of the team he/she cheers for.
2. (figuratively)A person who rallies support for any cause.

   “Given these sentiments, it is unsurprising that ultranationalists have been the main cheerleaders of closer Russia-North Korea relations.”