[5] Blumenfeld served as a law clerk to Judge Cynthia Holcomb Hall of the United States Court of Appeals for the Ninth Circuit from 1988 to 1989.

Blumenfeld was appointed to the Los Angeles County Superior Court by Governor Arnold Schwarzenegger on June 20, 2006, to succeed John Sandoz.

President Trump nominated Blumenfeld to the seat vacated by Judge Audrey B. Collins, who retired on August 1, 2014.

[7] On January 3, 2019, his nomination was returned to the President under Rule XXXI, Paragraph 6 of the United States Senate.

[10] On January 3, 2020, his nomination was once again returned to the President under Rule XXXI, Paragraph 6 of the United States Senate.