I can't find a simple list of his eight losing campaigns. I can see that he worked for Kerry in 2004, Gore in 2000, McGovern in 1972, Ted Kennedy in 1980, Bob Kerrey in 1992, and both Gephardt and Dukakis in 1988, but that only adds up to seven. It turns out he also worked on Ed Muskie's campaign in 1972.
To be fair, though, between the years of 1972 and 2004, the only two winning Democratic candidates were Jimmy Carter and Bill Clinton.
That's not "to be fair," that makes it so much worse! Between 1972 and 2016, he supported 8 losing Democratic campaigns and did not support any of the 3 winning Democratic campaigns? That's an extraordinary losing streak!
He retired before 2008, so Obama doesn't count. He worked for one of Clinton's primary opponents back when Clinton himself was a dark horse candidate, and he actually resigned from Carter's 1976 campaign after ten days, writing to the future President, "I am not sure what you believe in, other than yourself." So it basically boils down to, "he never worked for Jimmy Carter or Bill Clinton".
You could tell a similar story for any Democratic strategist with an overlapping career. Tad Devine worked for the failed campaigns of Mondale 84, Dukakis 88, Kerrey 92, Gore 00, Kerry 04, and Sanders 16. (He also worked in Ukraine on Viktor Yanukovych's winning 2010 Presidential campaign, alongside Paul Manafort. Small world.)
Also, if you work for a successful Presidential election campaign, you end up working in the White House, e.g. George Stephenapolous, Karl Rove, David Plouffe, David Axelrod, and Steve Bannon.
To be fair, though, between the years of 1972 and 2004, the only two winning Democratic candidates were Jimmy Carter and Bill Clinton.