With Iraq's government overthrown, Washington now sounds increasingly bellicose about Iran.
The US says Tehran is once again on the warpath
It is lobbying hard for Tehran to be referred to the UN Security Council for breaking agreements to stop nuclear development.
It wants fellow board members from the UN's nuclear watchdog, the IAEA, to take action against Iran when it meets on 13 September.
But after Iraq, will the rest of the world listen to the US cry of banned weapons of mass destruction?
And how far would the US act alone if its cry goes unheard?
'Changing the subject'
US President George W Bush revealed his view of Iran in 2002, when he named it, along with Iraq and North Korea, as part of the infamous "axis of evil".
"Iran aggressively pursues weapons [of mass destruction] and exports terror," he said.
Jon Wolfsthal, a non-proliferation expert at the Carnegie Endowment, agrees the Bush administration is turning up the heat, in part because "the process of uncovering Iran's nuclear programme is really coming to a head".
Iran's military capabilities have been worrying the US and Israel
He says it has become clear over the past year that Iran has, for the last two decades, kept large parts of its nuclear programme hidden.
"But," Mr Wolfsthal says, "I also think there is a bit of electioneering going on here in Washington."
He says the new focus on Iran could also be "an attempt by the Bush administration, which has had so much trouble in Iraq, to change the channel, to change the subject".
According to Mr Wolfsthal, the administration is now saying: "Things may not have gone the way we wanted them to in Iraq but we can't dwell on the past, we have other challenges we need to face and Iran is at the top of the list."
The US says Iran is working towards building nuclear weapons. But that has not been proved.
Tehran has broken agreements to stop building technology to enrich uranium.
But it is unclear whether Iran's goal is nuclear power, as it claims, or nuclear weapons.
Iran's nuclear reactor at Bushehr has attracted suspicion
Michael Levi, of the Brookings Institution, says the line between the two is easily crossed.
"We know some things they're doing now they weren't doing until recently, in particular assembling uranium centrifuges," he says.
"What we don't know is what they might be doing behind closed doors."
He says technology such as uranium centrifuges can be used for part of the nuclear power programme or as part of a nuclear weapons programme.
"It seems to be a consensus that at the very least these are part of a contingency capability - they could be redirected towards a weapons programme," Mr Levi says.
So with the case unproved but the US clearly convinced, what can Washington do?
The focus so far is on diplomacy.
Washington has been frustrated that some European countries, like France and Germany, have taken a more carrot than stick approach, focusing on engagement rather than punitive action.
But now even Europe may be running out of patience.
"The Europeans had been prepared to move forward on various things that they are certainly not prepared to move forward on now," says US State Department spokesman Richard Boucher.
"And to the extent that they have found their proposals rejected, that Iran has violated its own commitments... I think you'll find a more concerted attitude by all the nations as we head into the September meeting."
'Carping from the cheap seats'
The pressure is on. Many in Washington who criticised European countries for dragging their feet on Iraq are getting deja vu.
"My great frustration is that I think Iran is the 800lb gorilla in the corner of the room," says John Hulsman of the Heritage Foundation.
He accuses Europe of acting like Britain's pre-World War II Prime Minister Neville Chamberlain - waving agreements in the air while the threat grows.
The feisty US rhetoric, he says, is designed to shock Europe into action.
"They're raising the rhetorical tone to try to warn people that this is indeed a pressing issue and that the Europeans have to be serious at the IAEA meeting to begin to ratchet up the pressure."
This, he says, is because Europe will be as affected - if not more so - than the US by these developments.
The concerns are even more pressing now that the US has invested so much politically in Iran's neighbour, Iraq.
Colin Powell used his Iraq visit to warn Iran against interfering
When Colin Powell made a recent surprise visit to Baghdad, he issued a stern warning to Tehran not to add to Iraq's problems by fuelling dissent.
"Iran has the potential of playing a helpful role but we are uneasy about some of the actions Iran has been taking in the south," he said.
"We hope the Iranian authorities will realise it's in their interests to have a stable Iraq as a neighbour."
With Iraq still draining resources, the US has limited scope for another conflict.
Some analysts suggest strikes by Israel could do the job for them.
Appetite for a crisis?
Mr Wolfsthal of the Carnegie Endowment says cynics might even see the tough foregrounding of the threat from Iran as part of the President's re-election campaign.
"In a peaceful environment, people would say Bush has a very difficult time convincing voters he's the man for the job."
"The economy is still not doing very well, his tax policies haven't benefited the majority of Americans, we have a number of problems with health care."
Washington is lobbying hard behind the scenes - including in London.
But so far there is little indication of how eager the rest of the world is to get tough on Iran - and risk another crisis in the Middle East.