One of Hillary Clinton's biggest champions in labor during the primary, the American Federation of State, County and Municipal Employees (AFSCME), endorsed Barack Obama for president today. At the height of the primary contest, AFSCME was not only a fierce advocate for Hillary Clinton, but also a harsh critic of Barack Obama, so this endorsement serves as a sort of microcosm of the larger shift that we're seeing toward Obama by Hillary supporters. But as for many, this shift did not come lightly.

WaPo's The Trail spoke with AFSCME president Gerald McEntee, who was one of Obama's more vocal critics.

Today, McEntee sounded a much different note as he announced that his union -- the largest in the AFL-CIO, with 1.5 million members -- had endorsed Obama after supporting Hillary Clinton in the primary. "Barack Obama has mobilized a historic movement to reclaim the greatness of America," McEntee said. "With his leadership, our nation will rise up to rebuild the middle class at home and restore America's reputation in the world."

Obama, McEntee added, "is a proven fighter on the issues our members care about most, such as ending privatization, providing state and local fiscal relief, fully funding and supporting public services and the workers who provide them, and guaranteeing that everyone in our country has access to quality, affordable health care they can count on."

Asked about the change in his estimation of Obama from one month ago, McEntee said that he and other AFSCME officials had changed their views of the candidate after extensive meetings with his staff and with Obama himself in Washington yesterday and today. "We've had an opportunity ... to sort out our differences to move ahead," he said. "We have changed positions [on Obama]. He's more sure-footed. We fought like hell for Hillary, no question about that, and at times it was tough on the campaign trail, but now we're prepared and ready" to back Obama.

Today's endorsement is further evidence of a swiftly uniting Democratic Party behind Barack Obama and as if you needed even more proof, Fox News brings us this result from its latest national poll:

Most Clinton supporters strongly back Obama -- 68 percent, up from 47 percent in April. Still, 17 percent say they would vote for McCain if the election were today, and 15 percent are undecided.

We can expect that number to grow larger as Hillary Clinton starts appearing on Barack Obama's behalf as the summer progresses.