For decades, about the worst thing you could say to a politician was that he was behaving like Richard Nixon. A cunning "realism" and willingness to deal with dictators--from Beijing to Latin America to, yes, Iran--helped make the 37th president Public Enemy No. 1 on the left.

Post-Nixon presidents were forced at least to show deference to human rights. When the Shah of Iran was teetering, for example, Jimmy Carter chose not to embrace the ailing dictator as an ally. The U.S. allowed him to fall and thus helped give birth to the theocratic oligarchy that governs Iran to this day (and will continue to govern no matter how the recent election sorts out).

Today, Barack Obama is behaving like Mr. Nixon, and may yet suffer like Mr. Carter, in his attempts to deal with Iran in 2009.

The fundamental flaw in Mr. Obama's thinking on Iran--indeed, in his entire critique of George W. Bush's so-called freedom agenda--is that he implicitly accepts the legitimacy of the oppressive regimes he wants to engage. Just as Mr. Nixon and other old-style realists used to do, he wants to "deal with" an illegitimate and oppressive regime because it happens to hold power in Iran.

There are two problems with this.

No. 1 is that it puts him on the wrong side of history. The mullahs don't represent the Iranian people, as we have seen day after day in the streets of Tehran.

No. 2 is that it won't give him the desired result of curtailing Iran's nuclear program anyway. The mullahs invented the nuclear program, and they are not about to jettison it merely to win favor with Mr. Obama.

Indeed, given that the president waited 10 days to express outrage over the regime's bloody suppression of protesters, the theocrats probably now see him as someone they can count on to equivocate if they succeed in oppressing the protests against their rule.

Sen. John Kerry, Massachusetts Democrat and chairman of the Senate Foreign Relations Committee, also sounds strangely Nixonian these days. Mr. Kerry wrote in the New York Times on June 18 that Mr. Obama's "vision" and "outreach" had already made a difference in Lebanon and Iran.

"Returning to harsh criticism now would only erase this progress, empower hard-liners in Iran who want to see negotiations fail and undercut those who have risen up in support of a better relationship," Mr. Kerry wrote.

Sounds like realpolitik writ large.

Yet speaking in support of the struggle for freedom by the Iranian people isn't meddling: Ayatollah Khameini already made that charge against the U.S. in spite of Mr. Obama's reticence. Rather, it is an appropriate defense of the basic human rights that are being trampled in Iran--and nothing more.

In standing up for the principle of freedom, Mr. Obama need not endorse any particular presidential candidate in Iran. But he should say that the groundswell of support for former Prime Minister Mir Hossein Mousavi represents something much larger--the beginnings of the birth of freedom in Iran.

While it is true that Mr. Mousavi was a mullah-cleared candidate, and until recently, shared many of President Mahmoud Ahmadinejad's goals, it is now true that he has become a symbol of a challenge to the ruling clerical class. Iran may be entering a revolutionary period in which Mr. Mousvai and/or his followers question not only the outcome of the elections, but the very legitimacy of the regime.

It would be tragic for Mr. Obama to leave Iran and the world with the impression that he could have lived with Mr. Ahmadinejad's stolen election. He should seize the moment and the moral high ground by speaking directly to the Iranian people, reinforcing their desire for freedom and acknowledging that the regime doesn't enjoy international support.

The Iranians already have shown the regime doesn't enjoy internal support. They apparently would like to choose more moderate leaders--if the mullahs would let them be on the ballot.

Mr. Obama also should rally international support for effective economic and political sanctions on Tehran. He should call on European and other allies to impose the same level of economic sanctions that the U.S. has imposed on Iran since 1995.

Depriving Tehran's illegitimate government of a vital source of foreign investment, trade and loans would increase pressure on its leaders to change. They are unlikely to make concessions on the nuclear program or how they treat the Iranian people unless they are convinced their hold on power is at risk.

If Mr. Obama isn't careful, he'll end up with the worst of all possible outcomes: an even more oppressive regime strengthened by crushing the will of its people and armed with nuclear weapons.

To avoid that, he should repeatedly voice his support for Iranians struggling to reclaim their freedom. That would promote American ideals and universal human rights, as well as advancing U.S. national interests.

Iran doesn't have to be a threat to its neighbors, its own people and the United States. By standing up for the people of Iran, we are isolating not the country or people of Iran, but a regime that increasingly is seen as illegitimate by a sizeable segment of the Iranian people.

Iran will see its international stature improve when Iranians are free to pursue their own interests--not the narrowly defined interests of a radical regime. That's an outcome even Mr. Nixon and Mr. Carter could agree on.

Kim Holmes is vice president of foreign- and defense-policy studies at the Heritage Foundation.