ON THE WANE

- dimishing; failing
e.g.

NRA's political influence on the wane, says gun control advocate

The Current

http://www.cbc.ca/player/play/2690366970

or

I maintain that there is evidence to suggest that it is on the wane. I would argue, along with Morris Berman, in his book, The Twilight of American Culture, that it is.

https://books.google.com.br/books?isbn=076184676X