Obama has thrown a few bones to the “Occupy Wall Street” crowd, but so far he’s avoided explicit displays of support for the protests. But he might not be able to play the middle much longer, now that the labor unions, some of his biggest political supporters, are joining up with the activists:

Meanwhile, the Massachusetts Nurses Association says hundreds of the city’s nurses will rally with the Occupy Boston protesters on Wednesday. The association says the protest will be part of the opening day activities for a national nursing convention in Boston.

In New York, several unions endorsed the Occupy Wall Street movement and plan to join the protesters’ street theater Wednesday, labor leaders said.

Congressional Democrats are also throwing their support in with the protesters, reports The Hill:

“We share the anger and frustration of so many Americans who have seen the enormous toll that an unchecked Wall Street has taken on the overwhelming majority of Americans while benefitting the super wealthy,” Reps. Raul Grijalva (D-Ariz.) and Keith Ellison (D-Minn.) said in a joint statement. …

House Democratic Caucus Chairman John Larson (Conn.) released a statement Wednesday saying, “The silent masses aren’t so silent anymore. They are fighting to give voice to the struggles that everyday Americans are going through.”

Dave Weigel points out the movement’s poll numbers are surprisingly decent so far – 33 percent of American voters view them favorably, 27 percent unfavorably, with 40 percent undecided. Those numbers are far from a national endorsement of the protests, but they definitely aren’t a national rebuke either. Obama will be under increasing pressure from his base to support the activists, but he takes a risk if he does so. Just like Democratic strategists tried to tie any offensive signs at Tea Party rallies to the GOP establishment, anything negative that happens at Occupy Wall Street can become a liability for the president if he gives the protests his blessing.