Among the casualties of the Obama administration's Iran policy are certain weary but time-honored diplomatic cliches whose credibility has collapsed along with the administration's credibility itself. Thus, "on the table" means "off the table." "We will continue to carefully monitor" means "We will look the other way." And "We remain committed" means "You can pretty much forget about it."

The disintegration of American credibility in world affairs continued last week when the United States, having finally indicated on Wednesday morning that it would impose new sanctions on Iran for its violation of international restrictions on its ballistic missile testing, sent word by the end of the day that it had changed its mind.

In arguing for his Iranian nuclear deal last year, President Obama repeatedly assured Americans that, although the U.S. was handing over some $150 billion in sanctions relief to Iran under that deal, we would not hesitate to sanction Iran for its violation of other obligations — such as those contained in United Nations resolutions banning its ballistic missiles program. And, he reassured us, should Iran violate the nuclear deal itself, why, the sanctions imposed against it for racing to acquire nuclear weapons would simply "snap back."

If few people believed those assurances then, still fewer believe them after last Wednesday's debacle. In October and then again in November, Iran test-fired ballistic missiles, which the United Nations itself stated clearly violated its Security Council resolutions. The administration's own Treasury undersecretary put it plainly: "Iran's ballistic missile program poses a significant threat to regional and global security."

After weeks of temporizing, the White House released word last Wednesday that at 10:30 a.m. it would announce that sanctions would be imposed on Iranians involved in these violations. Then, at 11:12 a.m. it sent word that its announcement would be "delayed for a few hours." The last word of the day came at 10 p.m., saying that the announcement would be delayed indefinitely, and by Friday the White House was saying that it was still thinking about it.

What happened to cause the administration's reversal? The Iranians had responded to word of the original announcement by threatening to treat sanctions based on their missile program — which the White House had assured Americans was independent of the nuclear deal — as a violation of that deal. Faster than one could say "centrifuges," the Obama administration caved.

Democratic lawmakers who had bravely limited themselves to issuing platitudes about not trusting Iran before voting to hand it a path to nuclear weapons and billions of dollars with which to foment terror are now dusting off the familiar platitudes.

"I believe in the power of vigorous enforcement that pushes back on Iran's bad behavior," proclaimed U.S. Sen. Chris Coons (D-Del.). "If we don't do that, we invite Iran to cheat."

No kidding.

Iran banks on the Obama administration reliably overlooking its conduct, no matter how egregious, whether it is violating its international obligations or violating the nuclear deal itself. The White House touts its rapprochement with Iran as its landmark foreign policy achievement and, as Iran well knows, cannot afford to have it exposed in ways that tarnish it. And the White House banks on the American media being tired of the Iran issue.

In his memoir, Obama's former defense secretary, Leon Panetta, warned that the White House's tendency to retreat from its own promises seriously endangers national security.

"[T]he power of the United States rests on its word," writes Panetta, "and clear signals are important both to deter adventurism and to reassure allies that we can be counted upon."

This administration's embarrassing reversal on Iranian missile testing reinforces a legacy of toothless threats and meaningless assurances, which embolden enemies, dispirit friends and worsen a deepening threat to American security.

Jeff Robbins, a former United States delegate to the United Nations Human Rights Commission under President Clinton, is a Boston attorney. Talk back at letterstoeditor@bostonherald.com.