Sometimes we find that politicians, or anyone else, are not telling the truth, and nothing but the truth, so you use this expression. Read about what it really means.
The English we speak: It won't wash (BBC Learning English)
Articles related with the issue:
White House ‘systems failed’ with Comey firing, but Trump pushed the buttons (The Washington Post)
- Episode 170510 / 10 May 2017 >>> Expressions presented: condition, draw & is down to.