The mystery surrounding President Washington’s famous 1790 letter guaranteeing religious liberty in America continues.

As the Forward revealed last week, Washington’s letter to the Hebrew Congregation of Newport, R.I., disappeared from public view almost a decade ago, after the B’nai B’rith Klutznick National Jewish Museum, where the letter had been displayed for half a century, moved to a smaller location and put the document into an art storage facility in suburban Maryland.

The Morris Morgenstern Foundation, which owns the letter and loaned it to the museum, has kept such tight control over it that even top American Jewish historians had no idea where it was. Now one of those scholars has uncovered historical records detailing a secret tug-of-war between the congregation of Touro Synagogue in Newport and Morris Morgenstern, the New York philanthropist who bought the letter in 1949 at a fraction of what the iconic document is worth today.

Touro’s congregants considered themselves to be the historical heirs of the recipients of the original letter, in which Washington pledged that the new United States would give “to bigotry no sanction, to persecution no assistance.” Minutes from synagogue meetings, uncovered by a history professor at the University of Pennsylvania, show that Morgenstern originally considered loaning the letter to the congregation — and that the congregation simultaneously made preparations to sue Morgenstern to get the letter back.

Beth Wenger, director of Penn’s Jewish studies program, discovered the documents in the jumbled archives of Congregation Jeshuat Israel while she was researching her latest book, “History Lessons: The Creation of American Jewish Heritage.”...