Norm Eisen tweeted the remark as he shared a link to a story about Jared Kushner's sister highlighting her family ties as she wooed Chinese investors.
Mr Eisen is suing the President for allegedly violating the "domestic emoluments clause," which prohibits the President from receiving additional compensation besides his salary.
— Norm Eisen (@NormEisen)May 7, 2017
Mr Kushner said he stepped down as chief executive of Kushner Companies in January and sold stakes in several properties to allay concerns about conflicts of interest while he serves as senior adviser to his father-in-law, Donald Trump.
But his sister highlighted her ties to Mr Kushner as she made a pitch to raise funds from Chinese investors through the US government's controversial EB-5 visa programme, which gives permanent US residency to those who finance projects that create a certain amount of jobs.
The Kushner family's promotional efforts in China come amid widespread criticism of the EB-5 visa programme, which has grown popular among wealthy foreigners seeking to move to the US but faces allegations of fraud and misuse.
Critics say many of the investments purportedly aimed at assisting poor areas of the US have instead wound up going to projects in more affluent neighbourhoods, while many programmes have been badly hit by fraud scandals.
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Now led by Mr Kushner's relatives, Kushner Companies had earlier been negotiating with China's Anbang Insurance Group to provide what could be hundreds of millions of dollars in equity for redevelopment of a Manhattan office building.
Critics saw it as a potential attempt by China to curry favour with the White House.
The Chinese company's advertisements for the One Journal Square development in Jersey City described the project as "Kushner 1," with punchy subtitles declaring that it has "government support" and is "founded by celebrity developers," without elaborating.
Journalists were barred from the event.
Bi Ting, a 34-year-old woman who attended the Shanghai event, told the Associated Press having the name of the US President's son-in-law associated with it was "a bonus for the project."
Ms Bi said Mr Kushner's sister Nicole Meyer spoke for more than 10 minutes, describing the history of the Kushner family and the highlights of the project.
Additional reporting by Associated Press