The phrase "questionable legitimacy" is correct and usable in written English.
You can use it to describe a situation in which the legitimacy of something is uncertain, or in doubt. For example, "The origin of the product had a questionable legitimacy, so many customers chose not to purchase it."
If tainted, it would produce a government of questionable legitimacy.
It is a coercive enterprise of questionable legitimacy.
And Sir Jeremy Greenstock, a former ambassador to the UN, said he believed the invasion was legal but of "questionable legitimacy".
There were no close calls — no hits to the head that were of questionable legitimacy, no flags thrown that shouldn't have been.
But NewsNow decided to no longer include links to NLA member sites in its service saying the agreement was "unacceptable and of questionable legitimacy".
But Elizabeth's taunts sting Mary's pride, and she responds in kind, throwing Elizabeth's questionable legitimacy in her face, luxuriating in suicidal satisfaction.
Scottish ministers are to ban police from using stop and search without legal cause after an independent inquiry found it was of "questionable lawfulness and legitimacy".
Ministers agreed on Thursday to set up a new statutory code on police search powers and to discuss the need for specific powers to search children for alcohol after being warned by Scott that "non-statutory stop and search lacks any legal framework and is of questionable lawfulness and legitimacy, with poor accountability".
But it also suffered from political uncertainty: investors had to wonder whether a government that had a questionable claim on legitimacy, that had staked its claim to power mainly on its supposed ability to deliver prosperity, could survive a major economic downturn.
You questioned his legitimacy.
