cast doubt on
Cause something or someone to be questioned. For example, The prosecutor cast doubt on the wife's alibi. This idiom uses cast in the sense of “throw,” a usage dating from the early 1200s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.