ABC News' Z. Byron Wolf reports: More evidence of the fragility of Democrats’ health reform coalition comes today from Sen. Bernie Sanders, the liberal Independent from Vermont. Democrats will need Sanders – and every other Democrats’ and Independents’ vote – to overcome a Republican filibuster of health reform legislation. But Sanders said today he has not yet signed on to the latest push by Democratic leaders. “At this point I’m not on board,” said Sanders at a press conference called to outline his plans to derail the re-nomination of Ben Bernanke as Federal Reserve Chairman. Sanders did not say if he would join in a filibuster the bill or simply vote against it. Sanders said he is in discussions with Democratic leaders and the White House to tweak the bill so he can support the bill, but he is an avowed critic of a private insurance system. “The function of private insurance companies is not to provide health care it’s to make a profit,” said Sanders. His proposal, which does not have the votes to pass, but he offered anyway, was the subject of Republicans' first attempt at wholesale delay of Democrats’ health reform bill. As Sanders was giving his press conference, the Senate clerk was two hours into reading his 800 page bill to create a single payer system. “You at least have to provide real competition to the insurance companies,” said Sanders without elaborating on how that could be done short of a public health insurance option. Sanders jokingly thanked Sen. Tom Coburn, R-Okla., for insisting on the reading since it was getting the single payer proposal more attention. But he also pointed out that Republican obstruction is keeping Democrats from accomplishing much on the Senate floor. Sanders’ fellow Vermonter Howard Dean encouraged Democrats to kill the proposal by Democratic leaders because he said too much has been conceded to obtain the votes of conservative Democrats. Liberal Democrats have suggested circumventing Senate rules and utilizing budget reconciliation, which only requires 51 votes, to pass health reform proposals more to their liking. But party leaders seem to have decided that the reconciliation process would be long, complicated, create a patchwork bill, and perhaps lead to backlash among voters. On the other side of Democrat’s "big tent" is Sen. Ben Nelson of Nebraska. He hasn’t signed onto the deal yet, even though he was instrumental in stripping the public option, because he does not think a ban on using federal funds for abortions in the bill is restrictive enough.