Photos: Clinton and Obama campaign

It also failed to deliver the Nevada caucus to Sen. Barack Obama, even after an endorsement from the powerful Culinary Workers Union, the bedrock of workers in Las Vegas and Nevada's chapter of the Service Employees International Union (SEIU).

But Mr. Obama hopes the unions still have enough juice left to help him grab come-from-behind victories over Sen. Hillary Rodham Clinton tomorrow in Ohio and Texas, where the SEIU is spending $1.4 million on his behalf.

Union membership may have been on the decline in the past decade, but its numbers rebounded slightly in the past year and Democratic candidates still value the funding, foot soldiers and political advertising union backing can provide.

"We currently have over 1,000 members and volunteer staff in Ohio sending direct mail and making phone calls to several hundred thousand voters in the state," SEIU spokeswoman Stephanie Mueller said.

In Ohio, more than 40 percent of the party"s primary voters are from union families. To date, about three in 10 Democratic voters have come from households with at least one union member — and exit polls show they prefer Mrs. Clinton by about four percentage points.

Whether their electoral power is waxing or waning, unions still exert a strong influence on the positions the candidates take.

Mr. Obama, since scooping up endorsements from major umbrella organizations, has sharpened his attack of his rival"s support of the North American Free Trade Agreement (NAFTA) — through her association with the Clinton administration — that many union workers blame for the loss of factory work, particularly in Ohio and Pennsylvania.

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