Conversation so far:
Is Steven Spielberg affiliated with one political party?
Steven Spielberg has usually supported U.S. Democratic Party candidates.
Has Steven Spielberg made any films that are political?
Steven Spielberg directed an 18-minute film for the project, scored by John Williams and entitled The American Journey.
Is Steven Spielberg personal friends with any political figures?
Steven Spielberg has been a close friend of former President Bill Clinton
Has Steven Spielberg made campaign donations to any political figures?
Steven Spielberg has donated over $800,000 to the Democratic party and its nominees.
Is there anything especially noteworthy about Steven Spielberg's political beliefs or stance?
Steven Spielberg supported Hillary Clinton for President of the United States in the 2016 election.
Has Steven Spielberg used his fame in another other way to support a political cause?
In September 2008, Steven Spielberg and his wife offered their support to same-sex marriage by issuing a statement following their donation of $100,000 to the No on Proposition 8“
Is there anything else to know about Steven Spielberg and his political beliefs?
Steven Spielberg donated US$1 million to Priorities USA, a pro-Clinton Super PAC

Question: When did they make that donation?
Self-contained rewrite: When did Steven Spielberg make that donation?