A: After becoming president of the United States, Donald Trump promised several times to drain the swamp in Washington.

B: Politics is complicated. The president isn’t as powerful as he seems, and there is not really much he could do.

Note: This idiom means “to root out the practice of corruption or something that is harmful.” The origin is based on the practice of draining swamps as a way to lower mosquito-breeding and thereby fight malaria. One of the earliest uses of the idiom “drain the swamp” has been recorded as made by Winfield R. Gaylord, a politician. Clearly, given its metaphorical sense, the phrase has been used by and large by American politicians more than anywhere else, especially for the last few decades.