President Bush is again touring the country and reassuring Americans that democracy will triumph in Iraq and American troops will return victorious. Those admirable goals are made more difficult daily by sectarian violence.

He’s also changing the subject – to Iran, which Secretary of State Condoleezza Rice last week called the greatest threat to American security. Amid the d?j? vu, the question is whether the administration and Congress have learned lessons from the invasion of Iraq to better inform how the United States responds to Iran.

Also touring the country is Scott Ritter, a former chief United Nations weapons inspector in Iraq, who wrote in his recent book “Iraq Confidential” that the United States misused the weapons-inspection process to build a case that Iraq was a threat rather than to disarm the country. Mr. Ritter, who was in Maine this week, sees the Bush administration ready to make the same mistake in Iran. Congress should not blindly go along.

Although Iran has restarted its uranium-enrichment program, it is a long way from producing weapons. A first problem is that Iran’s uranium ore is contaminated with impurities. The uranium is turned to a gas, which is then spun in centrifuges for enrichment.

Contaminates clog the centrifuges and, often, break them. Iran could have gotten around the contamination problem by accepting Russia’s offer to enrich uranium there.

Twenty years ago, the Iranians secretly bought drawings and used centrifuge parts from Abdul Qadeer Khan, the Pakistani who ran a nuclear black market. They tried to buy better quality centrifuges from Russia, but the Clinton administration quashed the deal. That left Iran to copy the used parts it had earlier acquired.

According to the International Atomic Energy Agency, about 30 percent of the 164 centrifuges at an enrichment facility in Natanz were broken when operations were suspended there in 2003. Those centrifuges would have to be repaired before the process can begin again. Iran would also have to acquire or make tens of thousands of centrifuges to enrich uranium to make nuclear weapons.

U.S. intelligence officials say Iran is five to 10 years away from making fuel for a nuclear weapon.

Armed with this information, there’s plenty of time to proceed thoughtfully with Iran. Diplomatic efforts, so far led by the Europeans, have kept Iran engaged, if not compliant. If the country pursues its nuclear weapons work, a logical next step would be sanctions, which evidence shows were having an effect in Iraq, despite Bush administration assertions.

Arguments that Iran is sending fighters to Iraq are akin to the pre-Iraq invasion bluster that Saddam Hussein supported al-Qaida and had a hand in the Sept. 11, 2001 terrorist attacks in the United States. Members of Congress must see through the rhetoric and examine the facts before approving any kind of action against Iran.

There is growing support for Mr. Ritter’s view that invading Iraq was a mistake. The most recent AP-Ipsos poll found that only 39 percent of Americans support the way the president has handled Iraq. Nearly four out of five Americans, including 70 percent of Republicans, believe civil war will break out in Iraq.

The United States bumbled often in Iraq – from selectively using intelligence to justify military action to rid Iraq of non-existent weapons of mass destruction, to backing religious factions loyal to Iran. It can’t afford similar mistake again.