The first three grafs explain:

To win the House or pick up a significant number of seats in both chambers of Congress, Democrats will have to battle traditional allies in the labor and environmental community to win targeted races.

At least seven of the most vulnerable House GOP incumbents have been endorsed by unions, environmental activists or other Democratic-leaning advocacy groups. So have at least three of the most vulnerable Senate Republicans.

Organized labor has also poured tens of thousands of dollars into the campaign accounts of highly vulnerable Republicans, in several instances surpassing the amount given to Democratic challengers.

Defections by NARAL and the HRC, amongst others, have attracted blog attention. The union defections, not so much. (My impression, at least.)

There's a sourced allegation which isn't quite tied up (note to Matt: I'm not relying on it!) but which, if true, would place the malaise close to the House leadership:

Rep. George Miller (Calif.), ranking Democrat on the Education and the Workforce Committee, has disclosed that at least one of his House colleagues has said that, if Democrats fail to capture the House, labor will be partly to blame. Miller, a lawmaker close to House Minority Leader Nancy Pelosi (D-Calif.), shared that anecdote with labor officials, according to a union lobbyist, perhaps sending a subtle message of displeasure that Democrats know labor is hedging its bets.

That mention of Pelosi - just for the avoidance of doubt! - does not tag her with agreeing with the sentiment (supposedly) expressed by Miller. (These things need reading like legal small print!) But it certainly suggests an avenue for further research - not to mention, further worry!

The labor working both sides of the street hits lefty bloggers where they live:

Rep. John Sweeney (R), the Democrats' No. 1 target in New York, has won the endorsement of the local affiliate of the Laborers' International Union of North America and of the Albany affiliate of the Building and Construction Trades Department of the AFL-CIO, Sweeney's campaign says.

Union political action committees had given Sweeney's campaign $105,000 by the end of March, more than he had received from any other special interest. He received $10,000 contributions from the Laborers' Union, the United Brotherhood of Carpenters and Joiners, the International Brotherhood of Teamsters and the International Association of Fire Fighters, according to politicalmoneyline.com, a website that tracks fundraising.

LIUNA, Teamsters, IAFF no strangers to accusations of (and some convictions for) racketeering, the most cursory search suggests.

The blog connection?

The most recently filed fundraising reports for Kirsten Gillibrand, Sweeney's Democratic opponent, show that she has received only $32,000 from labor through March 31.

"We're really trying to work with incumbents and trying to not drink the Kool-Aid with some of the challengers," said one labor lobbyist, who added that Democrats can't expect unions to place all their bets on Democratic candidates and risk being shut out of the legislative process if they lose.

Gillibrand has figured here several times. And she's cute. (Damn those unions!)

Apart from Sweeney (no relation, I'm assuming!), the piece mentions Gerlach, Weldon, Shays, Nancy Johnson, Chafee and Conrad Burns as recipients of union largesse.

On the plus side (love those journos' idea of objectivity!) Ben Nelson

has been endorsed by several business groups, such as the U.S. Chamber of Commerce, the National Federation of Independent Business and the Business Industry Political Action Committee.

Whoopee!