In an op-ed in the Wall Street Journal on Tuesday, former Secretaries of State Henry Kissinger and George Shultz give a thumbs-down–as diplomatically as possible–to the new Iran nuclear deal-in-progress.

After reviewing the sorry history of failed diplomatic efforts to stop Iran, across several administrations, the two veteran diplomats describe the core of the problem with the agreement reached in principle in Geneva:

Under the interim agreement, Iranian conduct that was previously condemned as illegal and illegitimate has effectively been recognized as a baseline, including an acceptance of Iran’s continued enrichment of uranium (to 5%) during the agreement period….

Not surprisingly, the Iranian negotiator, upon his return to Tehran, described the agreement as giving Iran its long-claimed right to enrich and, in effect, eliminating the American threat of using force as a last resort….

The danger of the present dynamic is that it threatens the outcome of Iran as a threshold nuclear weapons state.

Kissinger and Shultz then recommend that the final agreement, to be negotiated when the six-month period ends (though we still do not know when it begins!), must “ensure the world’s ability to detect a move toward a nuclear breakout, lengthen the world’s time to react, and underscore its determination to do so.”

The U.S. should “be open to the possibility of pursing an agenda of long-term cooperation. But not without Iran dismantling or mothballing a strategically significant portion of its nuclear infrastructure,” they say.

This is about a charitable a criticism of the Iran deal as it is possible to provide. But when Iranian leaders are describing nuclear enrichment as a “red line”–taunting President Barack Obama in the process over his own failed “red line” against Syrian chemical weapons–it is clear that diplomacy will fail unless the U.S. can once again project an effective military deterrent. That requires a great shift that this president will not make.