“Twitter diplomacy” has never been conducted at such high levels. Iranian President @HassanRouhani, or someone very close to him, tweeted the news on Friday that he’d talked on the phone with President @BarackObama. Rouhani’s snippets of dialogue were at once awesome and anodyne. This was the first time the presidents of Iran and the United States have talked directly in the 34 years since the Islamic Revolution, and Rouhani emphasized the cordiality of the conversation. The two even joked about the traffic in New York. “Have a good day,” said the Iranian as he signed off. “Khodafez,” said the American, which is Persian for good-bye or, more accurately, “God be with you.”

Obama confirmed the conversation at a White House briefing. He’d talked with Rouhani about reining in Iran’s nuclear program, he said. And it appears they also discussed Syria, which was the subject of what Obama called another “major diplomatic breakthrough.” The hitherto dithering United Nations Security Council was preparing to vote unanimously for a resolution requiring the Assad regime “to put its chemical weapons under international control so they can ultimately be destroyed.” Rouhani quoted Obama telling him that if progress could be made on the nuclear file, “other issues such as #Syria will certainly be positively affected.”

But then the Rouhani tweets suddenly disappeared, deleted, and when the smiling Iranian president landed back in Tehran, protesters pelted him with eggs. Speculation is rife that they had the blessing of Iran’s Supreme Leader, Ali Khamenei, and the scene immediately raised questions about just how far Rouhani could go in any negotiations.

Such is the fog of diplomacy, especially when dealing with Iran. But from the seeming confusion and surprising successes of the last few weeks, a paradoxical axiom is emerging, and it’s an important one: America is rarely so powerful as when it threatens to use force, and rarely so weak as when it has actually used it.

When George W. Bush took over the presidency in 2001, the United States was without question the greatest power on earth, and with the greatest power to do good. But for Bush and his close advisors, especially the coterie around then-Vice President Dick Cheney, that wasn’t enough. They wanted to ram that fact down the throat of would-be rivals, like the Russians, and even longtime friends, like the French. It wasn’t sufficient, after the September 11 attacks, for the Bush administration to punish the Taliban and pursue Bin Laden in Afghanistan. It felt it had to launch a vast war to eliminate an imaginary threat in Iraq and establish an oil-pumping pro-American democracy there.

A decade later, after thousands of American soldiers and hundreds of thousands of Afghan and Iraqi civilians have died -- and trillions of dollars have been squandered -- the people of the United States feel deceived, disappointed and, indeed, bled dry by those seemingly endless, pointless military adventures. The depth of that public resentment was apparent over the last few weeks when Obama asked Congress to approve his plans for military action against the Syrian regime. The reaction was so negative that even hawks like Sen. John McCain looked like wet pigeons when their constituents got through with them. No more Middle East wars!

Yet, looking back at 2002, it’s apparent that the Bush administration could have achieved its most important stated objective -- making sure that Iraqi dictator Saddam Hussein did not have weapons of mass destruction – without firing a shot. And that depended on the threat of war. In 2002, much as Obama has done in 2013, Bush went before the United Nations General Assembly to demand action. “We will work with the U.N. Security Council for the necessary resolutions,” said Bush. “But the purposes of the United States should not be doubted. The Security Council resolutions will be enforced -- the just demands of peace and security will be met -- or action will be unavoidable. And a regime that has lost its legitimacy will also lose its power.”

Bush’s truculence galvanized what had been moribund diplomacy. Within weeks, United Nations inspectors were back on the ground in Iraq pursuing the most pervasive and invasive inspection regime in history. They discovered no weapons of mass destruction for the simple reason that there were none. But the Bush administration didn’t believe in those results, and ultimately didn’t care. It launched its war of “shock and awe” that began with an enormous bang and ended, eight years later, with whimpers.

Despite the handicap of this history, and the consequent resistance of the public, the Obama administration has managed to use the threat of force with impressive effect.

In the case of Iran, the administration has played the role of good cop to Israel’s bad cop. You may recall Israeli Prime Minister Benjamin Netanyahu’s speech before the United Nations a year ago, when he held up a cartoon image of a bomb and talked about where a red line should be drawn against Iran’s nuclear enrichment program. The Israelis have made it clear many times that they would regard a nuclear-armed Iran as a direct threat to their existence, and they are prepared to go to war to stop it.

The Obama administration, for its part, appears to be holding Israel back even as the president states bluntly that the United States will not allow Iran to have nuclear weapons and that “all options are on the table.” He is threatening, in effect, to join or even to lead a military operation if it’s the only option left.

Against that backdrop, the United Nations has imposed on Iran a collection of devastating sanctions that have crippled its economy and forced it to get a whole lot more serious about negotiations. Rouhani, who professes himself to be a great moderate compared to his predecessor, the gratuitously provocative Mahmoud Ahmadinejad, was elected in June by Iranians hoping desperately that he can get the sanctions lifted.

Since then Rouhani’s speeches, interviews and tweets certainly have created a better atmosphere. And Obama has reciprocated by acknowledging many emotional issues that Iranians have seen in the past as an affront to their dignity. In Obama’s address to the United Nations he all but apologized for American interference in Iran dating back to Washington’s role overthrowing Iran’s elected government in 1953, which was admitted by the CIA officially only this August.

In Obama’s remarks at the White House yesterday, he noted, “Iran’s Supreme Leader has issued a fatwa against the development of nuclear weapons. President Rouhani has indicated that Iran will never develop nuclear weapons.” But acknowledgment does not imply credulity. “I have made clear that we respect the right of the Iranian people to access peaceful nuclear energy in the context of Iran meeting its obligations,” said Obama. “So the test will be meaningful, transparent, and verifiable actions, which can also bring relief from the comprehensive international sanctions that are currently in place.”

“Trust but verify,” as Ronald Reagan once said while negotiating disarmament with the Russians. And with regard to Iran, yes, all options still remain on the table. Obama doesn’t need to keep repeating the threat for it to be effective. It’s there. Indeed, if negotiations fail, the fact that the Obama administration has been so polite and conciliatory should make it easier for it to win international approval for whatever steps it decides to take then.

On the Syrian front, the Obama administration has been quite explicit. When the Russians put forth their plan to freeze and remove or destroy the Assad regime’s chemical arsenal, White House press secretary Jay Carney said as flatly as he ever says anything that Moscow’s proposal came because of “the threat of military action." The binding United Nations resolution now agreed to by the Russians, who had vetoed even the blandest criticisms of the Syrian regime in the past, leaves the door open for multilateral military action under U.N. auspices if President Bashar Assad tries to back out of the deal.

Let’s hope that doesn’t happen. Obama almost certainly means it when he says he will use military force unilaterally, if necessary, to defend the “core” security interests of the United States. And at the U.N. this week he even seemed to embrace the notion, dear to U.N. Ambassador Samantha Power, that the United States has a duty to intervene in other countries to stop atrocities that do not affect, directly, American interests. In fact, Obama sounded a little like George W. Bush.

But there’s this difference: Bush used threats merely as the prelude to a war his administration was determined to fight no matter what. Obama is using the threat of war to achieve goals that actual military action rarely achieves, and so far he seems to be succeeding. To paraphrase the famous line from Clausewitz, Obama’s diplomacy is war by other means.