Plausible (but unsubstantiated) claims in a controversial debate

One rhetorical manoeuvre I've noticed is the following. A contentious claim - usually of political nature - is made. However, when the claimant is asked for evidence, they respond by saying that, while their claim is true, it isn't obvious enough to the casual observer to be substantiated. In practice this involves claiming that something is "covert" to avoid giving proof of its existence.

Right-zionists have come up with the concept of New Antisemitism, which is a covert form typically disguised by 'criticism' of Israel and its government. This allows them to assert that a given opinion or expression is antisemitic, but when asked for proof, simply claim that it is 'covertly' so and thus no further proof is needed. Since covert antisemitism is a legitimate concept, it is hard to dispute the allegation.

Some left-feminists use the same logic with regards to sexism, and racial equality activists use similar logic with regards to racism. Both groups here push the concept of 'microaggressions', which are covertly bigoted statements that accumulate to build an experience of oppression.

Logical form:

Claim X is made.

Evidence/proof for X is demanded.

Claim X is clarified/revised to now include the fact that it is 'covert', not overt.

Thus, no evidence for X is needed.

Claim X is asserted as true.