Elias Sander — the "s" was added in this country to the surname,— emigrated from Poland in 1921. He was 17.

"[Elias Sanders] and his brother came to the United States, and three [siblings] remained in Poland and of course they and their families all died," Larry Sanders said. source

Eli Sanders, U.S. senator Bernie Sanders' father, left his family in Slopnice, a rural village in the South of Poland, and immigrated to the United States. During the Nazi occupation of Poland, Slopnice’s wide-open fields were used for airdrops before the businesses and goods of the town’s local Jews were closed and confiscated. Most of Eli’s family was sent to concentration camps where they were killed.

On Aug. 29, 2013, the U.S. senator, his brother, and their wives returned to Slopnice, where the mayor, Adam Soltys, greeted them as dignitaries and showed them around the sleepy village. The group was taken to the town’s war memorial, two of the local schools, and even the place where the Sanders family home once stood. They were shown the official documents and photographs of the house, preserved in Slopnice’s archives, which the visitors kept as souvenirs. Source

U.S. senator Bernie Sanders is the son of Dora/Dorothy (Glassberg) and Eli Sanders. His father was a Polish Jewish immigrant. His mother was born in New York, to Russian Jewish parents.
Bernie’s paternal grandparents were Leon Sander and Ettel “Ethel” Horn.
Bernie’s maternal grandparents were Benjamin Glassberg/Glassburg (the son of Abraham Glassburg) and Brayna “Bessie” Greenberg. Source

פ"נ
אליהו ב"ר יהודה
נפ' ה' אב תשכ"ב
Elias
Sanders
Beloved Husband
And Father
Died Aug. 4, 1962
Age 58 Years
ת נ צ ב"ה

https://www.findagrave.com/memorial/99399040/elias-sanders