Correction: there are only 48 Democrats in the Senate.

It doesn't matter who the Independents caucus with. They are not Democrats. And one of them, Lieberman, is threatening to filibuster any bill that contains a public option. Lieberman is not a Democrat, so you can't blame the Democrats for his stupidity.

If ALL of the Republicans would support a filibuster by Lieberman (and they do), then the Republicans are perfectly able to kill the public option against the wishes of the majority of Democrats.