DY, Thanksgiving was never a religious holiday, despite the Pilgrim myth.vRabbi Hutner had to have been given wrong information.
The first Thanksgiving Day was declared by the first US Congress in 1789, but it was a onetime celebration.
The second was declared in 1863 during the Civil War by Abraham Lincoln. It was not formalized by legislation until the early 20th century.
There is an interesting, Jewish aspnet ct to the 1789 Thanksgiving. Southern congressman opposed the resolution on the grounds that declarations of thanksgiving was a common practice of European monarchs. A Connecticut congressman argued that , on the contrary, they were following the example of King Solomon and the dedication of the Temple. The Southerners replied that they could accept Solomon as the role model and voted in favor of national day of Thanksgiving ( to thank Hashem for the Constitution )