WASHINGTON — Stephen Miller, one of the key architects of President Trump’s hard-line immigration agenda, is the descendant of Jewish immigrants who arrived to a welcoming United States at the turn of the 20th century.

But in an essay posted online Monday, Dr. David S. Glosser, Mr. Miller’s uncle, argues that the family would have been turned away if the immigration policies currently backed by Mr. Trump and Mr. Miller were in place at the time.

“I have watched with dismay and increasing horror as my nephew, an educated man who is well aware of his heritage, has become the architect of immigration policies that repudiate the very foundation of our family’s life in this country,” Mr. Glosser wrote in the article, published Monday by Politico.

The article was a notable rebuke by a family member to Mr. Miller, who is one of the most fervent public defenders of Mr. Trump’s immigration policies — the ban on travelers to the United States from several Muslim countries, the separation of families crossing the border illegally and the drastic reduction in the number of refugees admitted to the United States.