Russian equivalent of "Elephant in the room"

Question

What is the Russian equivalent of the English idiom elephant in the room which means (according to Wikipedia)

important or enormous topic, question, or controversial issue that is obvious or that everyone knows about but no one mentions or wants to discuss because it makes at least some of them uncomfortable and is personally, socially, or politically embarrassing, controversial, inflammatory, or dangerous.

Just recently I heard on some news station something like this:

The obvious elephant in the room is president Biden's mental condition.

The only thing that comes to my mind are the emperors's new clothes (новое платье короля) from the fairytale by Hans Christian Andersen.

Answer 1

There is no exact Russian analog, not that I'm aware of, but a thing close enough would be скользкая тема or щекотливая тема:

А вот о политике, зарплате или музыкальных пристрастиях лучше не спрашивать. Слишком это щекотливые темы. И опять мы видим здесь общий принцип отношения к людям. // [Софья Тарасова. От Москвы до самых до окраин // «Знание - сила», 1998]

Щекотливую тему доступа к недрам осторожные аппаратчики не стали развивать ― пусть президент сначала примет политическое решение. // [Елена Короп. Аппарат правительства переписал среднесрочную программу Минэкономразвития, чтобы не испугать президента // «Известия», 2003.10.03]

These idioms lack the notion of "important or enormous" which is present in the English one, though.

Answer 2

Yellow Sky correctly referred to fact that expression is well known from a fable. The stable expression is «Слона-то я и не приметил» - "But I didn't spot the elephant", and there is no room mentioned.

If you want to preserve scathing style of statement in Russian, "непримеченный слон" (archaic), "незамеченный слон", although it can be hard to connect with "mental state" stylistically. Also, this is not exact analog. The American expression suggest the fact of ignoring something, while Russian suggest inability to spot something obvious.

As first use of "elephant in the room" got murky origins in 20th century and usually щы associated with ignoring the elephant in the room occurred in the 1935 Broadway musical, Jumbo. The character is stopped by a cop while leading a live elephant across the stage. “What are you doing with that elephant?” the policeman asks. “What elephant?”

So Russian expression refers to "obvious elephant" not to "ignoring elephant"

A non-meme way to convert the latter would be some analog: "Всеми игнорируемый фактом, аспектом, и т.д. является... " (A fact, aspect, etc. ignored by everyone is...)

Answer 3

I can suggest some more alternatives: больное место; больная тема; головная боль; бельмо на глазу; заноза; деликатный вопрос; острая тема; табу.