Back when the Bush administration was planning the Iraq war, the demise of Saddam was meant to have a ripple effect on other rogue states.

Especially states that helped terrorists and were building nuclear weapons.

Neoconservative pundits predicted that Iraq’s neighbor Iran, another member of the President’s “axis of evil,” might also undergo regime change.

But the ripple effect has boomeranged.

President Bush’s gross miscalculations about Iraq have emboldened Iran’s mullahs. The cost of these mistakes was in full view this week.

Iranian leaders defied U.S. and European warnings and restarted early stages of producing nuclear fuel that can be diverted to make atomic weapons. They believe the Iraq quagmire has deprived the United States of the option of bombing their nuclear facilities.

They are right.

There is good reason to be worried about Tehran’s nuclear program, despite Iranian claims it is only for peaceful energy purposes.

No expert I’ve talked to doubts Iran wants to develop at least the capacity to manufacture weapons. Iran’s ruling clerics hid key parts of their nuclear program for years. Add to that the fact that Iran helps groups that commit terrorist acts, such as Hezbollah and Hamas.

This is not a country that the world should want to see in possession of nuclear bombs.

But the U.S. presence in Iraq has made it more, not less, likely that Iran would go all out to develop weapons. Hawkish U.S. pundits boasted that Iran was the next regime that would topple after Saddam fell. Iraq was seen as a perfect base for overt or covert pressure on Tehran. Iraqi democracy was supposed to inspire Iran’s restless Shiite population to topple the mullahs.

Given such predictions, and 140,000 U.S. troops next door, it’s little wonder Iran is determined to produce fuel that could be used for nuclear weapons – and has so far rejected offers by the European Union to trade economic goodies for an agreement to stop producing that fuel.

But there are additional reasons why the Iran theocracy feels it can take this gamble. For one thing, flawed elections just returned a conservative new president, Mahmoud Ahmadinejad. The Iranian public has shown no interest in an uprising; they fear Iraq-style chaos.

For another, Iran’s regime has thousands of agents inside Iraq who could cause havoc for U.S. troops there if they chose to. They could do the same in Afghanistan.

And then there is the fact that Iraq’s government has developed the closest of ties with Tehran. Iraq’s Shiite leaders know they’ll need Iranian support if U.S. troops leave – to prevent a return of Sunni Baathists.

Iraqi Prime Minister Ibrahim Jaafari, who stood beside President Bush in the White House, recently visited Tehran and signed a raft of economic and military agreements. Iraqi Vice President Adel Abdel Mahdi told me in Baghdad last month: “Iran is very important for us. Any negotiations between Iran and the United States affect us, because both are our partners.”

In other words, Iraq’s Shiite majority would vehemently oppose any U.S. strikes against Iran. Nor would the United States win international support for bombing Iranian installations, especially since the bomb threat doesn’t appear urgent.

American intelligence agencies – burned by their Iraq experience – just issued a cautious assessment on when Iran will have weapons, saying it probably won’t get nukes until early in – or the middle of – the next decade. Previous U.S. estimates – and those of Israel – had placed the likely date sooner.

Vice President Cheney has suggested that Israel might “decide to act first” against Iranian sites. Israeli sources tell me that is unlikely.

At best, international pressure may get Iran to restore a temporary freeze on producing nuclear fuel. But the chance of halting the Iranian program probably ended with the Iraq invasion. Another unintended casualty of miscalculations about Iraq.

– Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer.