"The 25 Most Influential Liberals In The U.S. Media" (2009) by ancestry

The first list of influential liberals I found, from Forbes.

The exercise is subjective, by definition, and Forbes Opinions editors canvassed the views of more than 100 academics, politicians and journalists. The list that follows is a distillation of that survey.

Jews make up over half the list. Apart from Jews, non-whites, Irish Catholics, and a Greek, we have:

13. Bill Moyers Host and commentator, Bill Moyers’ Journal ["Born Billy Don Moyers[1] in Hugo in Choctaw County in southeastern Oklahoma, he was the son of John Henry Moyers, a laborer, and Ruby Johnson Moyers. Moyers was reared in Marshall, Texas.[2]" Enough said.]

21. James Fallows National correspondent, The Atlantic ["born in Philadelphia, Pennsylvania, the son of Jean (Mackenzie) and James Albert Fallows, a physician"; mother has a Scottish name; looking at his father's ancestors going back a couple generations, I find ancestors from Pennsylvania, Virginia, and Germany, but none from New England; update: I've now checked farther back on both sides, and find German, Scottish, and non-Puritan English ancestry; I've continued to find no New England ancestry, and can rule out any meaningful Puritan contribution.]

23. Kevin Drum Blogger, Mother Jones [You can see his ancestry here, directly from him. 3.5/8 of his ancestors appear to be Irish Catholic and 3/8 German or Swiss; at most 1/4 of his ancestry is colonial American, with half of that being Pennsylvania German; he has one great-grandparent born in Connecticut, but with a Scottish name, so unlikely to be of entirely early Puritan ancestry.]

24. Kurt Andersen Writer and host, “Studio 360? [born in Omaha, Nebraska; Scandinavian name; update: I checked his twitter account, and based on comments he's made Andersen is 3/4 Danish and 1/4 German, confirming he has no Puritan ancestry]

So even limiting our consideration to the 4 apparent NW Europeans on the list who don't identify as Irish Catholic, we see vastly more Southern and mid-Atlantic ancestry than New England ancestry, and more known or likely German, Scottish, and Irish ancestry than Puritan ancestry. The people who imagine Puritan descendants form a dominant segment of modern leftists for the most part have no idea what a descendant of Puritans actually looks like. They simply circularly identify northern liberals as "descendant of Puritans" and ignore southern liberals, while frequently trying to rationalize away the very obvious actual trends in ethnic overrepresentation.

Jewish:
1. Paul Krugman Op-ed columnist, The New York Times
3. Fred Hiatt Editorial page editor, The Washington Post
4. Thomas Friedman Op-ed columnist, The New York Times
5. Jon Stewart Host, The Daily Show
7. Rachael Maddow Host, The Rachel Maddow Show [1/4 Jewish; raised Catholic]
8. Joshua Micah Marshall Founder and editor, Talking Points Memo
9. David Shipley Op-ed editor, The New York Times
14. Christopher Hitchens Writer [3/16 Jewish; born in England]
16. Matthew Yglesias Blogger, ThinkProgress [1/2 Jewish]
17. Hendrick Hertzberg Columnist, The New Yorker [1/2 Jewish]
18. Glenn Greenwald Blogger, Salon.com
20. Gerald Seib Executive Washington editor, The Wall Street Journal
22. Ezra Klein Blogger and associate editor, The American Prospect
25. Michael Pollan Writer and journalism professor, University of California, Berkeley

Non-white:
6. Oprah Winfrey Presenter, The Oprah Winfrey Show
10. Markos Moulitsas Zuniga (“Kos”) Founder and publisher, Daily Kos
11. Fareed Zakaria Editor, Newsweek International

Irish Catholic:
12. Chris Matthews Anchor, Hardball [mother is Irish Catholic; father's parents are English from England and Northern Irish from Northern Ireland]
15. Maureen Dowd Op-ed columnist, The New York Times
19. Andrew Sullivan Senior editor, The Atlantic The Daily Dish

Greek:
2. Arianna Huffington Founder and columnist, The Huffington Post