water off one’s back
木曜日、元米大統領ブッシュ氏、オバマ氏が講演し、そろってトランプ大統領を非難しました。
Bush, Obama blasts will be water off Trump's back
(CNN)The Presidents club is turning on its newest member.
Breaking the code of silence that retired commanders in chief normally maintain about their successors, both George W. Bush and Barack Obama delivered clear jabs at the current occupant of the Oval Office on Thursday.
President Donald Trump, however, likely didn't feel a thing. His entire political brand stands as a living rebuke to the political establishment that both men once led and to the traditionalists who believe his behavior is eroding the prestige of the presidency itself.
waterを『ジーニアス英和辞典』で引くと、(like) water off a duck’s backという表現が載っています。上記ではduckがTrumpに置き換えられていますが、意味は（忠告・非難・侮辱が）何の効果もない、馬耳東風で、カエルの面に水で」となります。由来をインターネットで調べると、カモの背の羽毛は油性で水をはじくことかきているようです。(Kiwi girl)
