The court’s move comes against the backdrop

English as a Second Language English Vocabulary, Grammar and Idioms
1

The court’s move comes against the backdrop of a rapid shift in public attitudes about same-sex marriage, with recent polls indicating that a majority of Americans support allowing such unions. After the elections last month, the number of states authorizing same-sex marriage increased by half, to nine.

What does the bold part suggest?

2

A backdrop means a background - the things that are happening in the world when this action takes place. So the article is saying that the public’s attitudes are changing rapidly and that might have an effect on the court’s decision.