Tasini has scheduled an announcement for Tuesday morning in New York City, setting up a campaign that could put unexpected pressure from the left on Clinton, the unannounced frontrunner for the 2008 Democratic presidential nomination who until recently has been one of the strongest Democratic backers of the U.S. invasion and occupation of Iraq.

Tasini plans to campaign in support of the call by U.S. Representative John Murtha, D-Pennsylvania, for the rapid withdrawal of U.S. troops from that Middle Eastern country.

"Senator Clinton is out of step with the values of a majority of New Yorkers. While a majority of New Yorkers support an end to the war, Senator Clinton has repeatedly voiced her support for a war that continues to accumulate unacceptable costs, in terms of American and Iraqi lives and our own government spending," explained Tasini, decribing a central theme of a campaign that is also expected to advocate for fair trade, economic reforms and universal health care.

Clinton has felt little heat so far from her most prominent Republican challenger, Westchester County District Attorney Jeanine Pirro, whose campaign so far has been so hapless that some top Republicans are now calling for her to quit the race and instead run for state Attorney General.

But Tasini, who served for more than a decade as head of a national union and has since worked as president of the Economic Future Group, poses a far different and potentially more interesting challenge to Clinton. An author and frequent guest on television public affairs programs, Tasini runs a well-regarded progressive blog, Working Life, at his www.workinglife.org website, where his reviews of trade, health care and labor policy issues have drawn a broad following.

Unlike Pirro, Tasini understands the issues, he's quick on his feet, he knows his way around the state's union halls and he recognizes that Clinton's greatest vulnerability is a cautious centrism that has frequently put her at odds with grassroots Democrats.

Striking a chord that may well resonate with Democratic activists, Tasini says, "My candidacy will borrow a phrase from the late Senator Paul Wellstone, asking New Yorkers to'vote for what you believe in.'"

Even in liberal New York, a Tasini win in next September's Democratic primary would be a huge upset.

Clinton has a deep-pockets campaign treasury, a solid Senate record and an appeal to many Democrats who see her as both an heir to her husband Bill Clinton's legacy and potentially the best candidate to carry that legacy forward as a 2008 presidential contender. She also has an approach to even the most critical issues of the day that might charitably be referred to as "flexible."

In 2002, Clinton broke with more progressive Democrats such as Wellstone, the late senator from Minnesota, Massachusetts Senator Ted Kennedy, West Virginia Senator Robert Byrd and Wisconsin Senator Russ Feingold, to support authorizing President Bush to use force in Iraq. And during the 2004 presidential campaign, she echoed the sentiments of the most hawkish Republicans when she criticized Bush for not sending enough troops to Iraq.

But, as the war has lost popular appeal, Clinton has begun to blur her position. In a November 30 letter to constituents, the senator seemed to back away from her support of the 2002 resolution, writing, "I voted for it on the basis of the evidence presented by the Administration, assurances they gave that they would first seek to resolve the issue of weapons of mass destruction peacefully through United Nations sponsored inspections, and the argument