White House Press Secretary Robert Gibbs on Monday declined to reaffirm President Barack Obama’s pledge not to raise taxes on families earning under $250,000 per year, calling questions about the promise — asked in the context of a possible tax on health benefits — speculative.Gibbs asserted it would by “hypothetical— to talk about raising health benefit taxes because lawmakers have not approved health reform legislation and Obama has not yet been put in the position of having to decide whether to back such a tax“We’re going to let Congress do its job,— Gibbs said.During the presidential campaign, Obama used his pledge not to tax health care benefits to bash his opponent, Sen. John McCain (R-Ariz.), who said he would include the tax as part of his health plan.Democratic Senators have suggested in recent weeks that they may tax health benefits as a way to help pay for health reform. Obama and White House officials have not ruled out accepting such a move. Most unions firmly oppose the tax.