"Unless" war is necessary? -- or until?

Like Peter Beinart, I'm mildly heartened by evidence that "Obama's backbone vis Bibi [is] proving infectious" on Capitol Hill.  Yet  I'm troubled by a perhaps random note in Barney Frank's otherwise forceful message to Bibi to back off (as reported by the Hill's Julian Pecquet):

''Maybe Netanyahu's for (Republican candidate Mitt) Romney. And he's making a mistake if he is,'' Frank told The Hill when asked why he thought Israel had leaked the news of a perceived ''snub'' to the Reuters wire service.

''I think it was unwise for him to do as much,'' he said. ''I think they've pulled back a little bit.''

''I think Obama played it right,'' Frank added. ''The Israelis have to consider American public opinion; America's not ready to go to war until it's absolutely necessary.

 "Until" it's absolutely necessary, Barney -- not "unless"?  While Netanyahu has failed in his maximalist goal of making Obama move up his "red lines" for Iran, from producing a nuclear weapon to some ill-defined earlier stage of breakout capacity, the net result of the pressure has been to further harden Obama's commitment to strike at Iran if it does go nuclear -- in other words, to take containment off the table (which admittedly, Obama already had done).  And whatever modicum of "backbone" a few in Congress may be showing with regard to optics, the Senate, jumping about as high as Bib demands, just passed on a 90-1 vote a resolution stating “it is a vital national interest of the United States to prevent the government of Iran from acquiring a nuclear weapons capability” -- capability, not a weapon per se, which the hawkish Jerusalem Post regards as in accordance with Bibi's red lines demand. The resolution also explictly rules out containment as an option.

Until, indeed.