On the larger question of whether Trita Parsi functions as a lobbyist for the Iranian regime, based on what I know, I'd have to say yes: He has argued consistently against any sanctions against Iran, and an end to sanctions is obviously what the Iranian regime wants. So he is working on behalf of a stated interest of the Iranian government.
If by "the regime" you mean Mousavi and Karroubi, then I guess Jeffrey's right. But if Karroubi and Mousavi are "the regime", then the entire matter of the Green Revolution was utterly irrelevant, right? And yet it wasn't. At all.
On the specific matter of Trita Parsi: I have no long-term knowledge of the dude (and for quite a while thought he was a woman) and have never met him. I just know that when the Dish was covering Iran's revolution, few people were as committed or as devoted to the Greens as Parsi or his organization. To conflate him with the dictators he so actively exposed and resisted and who murdered or tortured people he loves and cares about is just wrong. After the trauma of last June, it's deeply hurtful and offensive.
And Parsi's opposition to sanctions reveals something essential to understand about Iran now: Mousavi and Karroubi, if allowed to take their rightful offices, would almost certainly have been as passionate in defending Iran's nuclear options as Ahmadinejad. In fact, in the latest round of negotiations, Ahmadi may be the most amenable to a nuclear deal - because it would give him some breathing space at home. Mousavi would have been totally constrained as president given the need to shore up his nationalist credentials. That's why Daniel Pipes and many neocons wanted Ahmadinejad to win. Anything else would complicate a policy of isolating, suffocating or bombing Iran to delay its nuclear capacity. And complicate it it has.
All of which is to say: the US's main opponent in preventing Iran's military nuclear development is ... the Iranian people.
Yes, the neocon analysis once again falters when it reaches the ground. It is extremely difficult to support the Greens and yet also support a military strike (which the Greens vehemently oppose) or more punitive sanctions (which Mousavi and Karroubi also oppose). And yet this seems lost on many in Washington. And I fear they are making the same mistake we made in the past (and I totally include myself). That mistake is in projecting onto people we do not know our own views about what is in their best interest.
The world is not as we may want it to be. Iranians are also a proud people, members of an ancient and noble and great civilization that is clearly asking for greater respect from the countries of the world, and see a nuclear capacity - for energy and bombs - as integral to that respect. Even if there is a democratic transition, that will remain the case. And Iran would become a very different and very Muslim democracy - and probably just as vehemently anti-Zionist - than any Western version. The neocons keep talking about the Middle East as if it were Eastern Europe after the Cold War. It clearly isn't. Culture matters. Religion matters. Pride matters. History matters.
Of course, all this leads to a highly problematic set of choices. If the Iranian people continue to believe in their nuclear capacity, if their loathing of Ahmadinejad continues to be tempered by their disdain of Israel, then it will be very, very hard for the United States to persuade Iranians that Israel has the right to 150 nukes and they have none. If the Green opposition were actively opposing the nuclearization of Iran, it would be one thing. We could leverage the people against the regime. But we are trying to leverage the regime in the one area where all the internal pressure is for Iran to be tougher with the US. If this is the main focus, we will end up strengthening Ahmadi, not weakening him.
But can we tolerate what that really implies - a nuclear balance in the Middle East between Israel and Iran? I should say I trust Israel infinitely more than Iran on using nuclear weapons. But the question is also harder than this. If Iran's acquisition of a nuclear bomb is inevitable at some point, and I suspect it is given their technological sophistication and educated populace, should we draw a line in the sand forbidding it? Or should we take a leap of faith and leverage a nuclear deal that includes aggressive monitoring with an end to sanctions as a sop to the opposition?
I'm not saying this is an easy choice. But it is the actual choice in front of us. Better to discuss this openly than cling to rigid ideological positions which have much more to do with us, than with them.