I guess he finally realized that it was moving from long-shot to fiasco:

Harold E. Ford Jr., the former Tennessee congressman who has sought to parlay his star power and Wall Street connections into a political career in New York, has decided not to challenge Senator Kirsten E. Gillibrand in the Democratic primary this September, according to friends and advisers.

After traveling the state on a closely watched tour, he told friends that he could prevail but feared that an ugly campaign would leave the winner drained of cash and vulnerable to a Republican challenger at a time when the Democratic Party controls the United States Senate by a slender majority.

“I’ve examined this race in every possible way, and I keep returning to the same fundamental conclusion: If I run, the likely result would be a brutal and highly negative Democratic primary — a primary where the winner emerges weakened and the Republican strengthened,” Mr. Ford wrote in an opinion article to be published in The New York Times on Tuesday.

Don’t let the door hit you on your butt.