When Saddam Hussein invaded Iran, one of my Iranian friends in Europe who was vehemently against the (Islamic) regime went to the Iranian embassy in London and volunteered to join the army and fight against Saddam! I think this says it all, when it comes to nationalist fervor, Iranians will forego their hatred for the regime and 'fight for Iran' and 'Iranians'.
There is no secret that the U.S. has been waging a cold war against Iran's mullahs for decades. The Irony of it all, is that in fact the Mullahs were put in place by the U.S. to begin with, and there have been tacit, secret backroom dealings with the Mullahs for decades. (Much like the Taliban, the U.S. later regretted that move, but it's a fact.)
But this war has now taken a new dimension with the rise of Donald Trump and his iranophobic administration. There is no secret about it; Mattis, Flynn, etc., are all staunch anti-Iranians along with many key Trump advisers like Giuliani, Kissinger, Bannon, etc. Trump's own rhetoric has also been very Iranophobic! For example, in his interview before the Super Bowl with Bill O'Reilly he mentioned Iran several times in a negative light.
There are two problems with all this "Iranophobia". 1. They are throwing the people of Iran out with the bathwater; i.e., with the Mullahs (and the regime) and 2. It's hollow. There is no possibility (especially in the near term) of an invasion or war with Iran. None. (Whom is he fooling?)
There are other problems too. In the race to threaten the regime in Tehran the U.S. is now aligning itself with nasty actors like the MEK/MKO/NCRI/RAJAVIST/MONKEYS (who are widely despised by the ordinary people of Iran), as if they are the only opposition to the Mullahs (and they are not). AND, the U.S. is also aligned with leaders in other countries like the Saudi Royals, Israel's Netanyahu, etc. (and even at one point Saddam Hussein), that are widely despised by the people of Iran. The U.S. has also been directly identified with supporting nasty regional terrorist groups like ISIS, and at one point in the past the Taliban (both also despised by the people of Iran). Moreover, Trump (and his Republican cohorts) are taking direct actions to isolate and alienate the people of Iran (the travel ban, and the rhetoric: calling Iranians liars, cheats (on the nuclear deal) etc.)
The people of Iran don't have to listen to the anti-U.S. propaganda from the regime in Tehran to identify friends or enemies; they can read social media and western news sites, i.e., U.S. news outlets to make up their own minds about who their friends really are!
News of Israeli atrocities committed by Netenyahu appear everywhere -- even western media. News of Saudi Arabia's indiscriminate bombing in Yemen appear everywhere. News of Iranians dying in Saudi Arabia while on a pilgrimage appeared everywhere. Pictures of ISIS fighters armed with U.S. weapons, and riding Toyota trucks with U.S. (plumber's) insignia, appeared everywhere. Facts about MEK/MKO/etc. support for Saddam Hussein are well known. I mean, you can look beyond the regime's propaganda and get to a conclusion that yes, Americans hate ordinary Iranians.
Iranians everywhere -- in Iran, in Europe, in the U.S., feel badly abandoned and isolated. It affects their daily lives. It affects them in everything they do. The net result is that the U.S. is alienating a badly needed ally -- the ordinary people of Iran... Iranians!!
If there is a plan to invade Iran, the U.S. will need the support of the people of Iran. All of them. Otherwise, the U.S. will find itself in the same situation that Saddam Hussein was in when he invaded Iran: the people of Iran abandoned their hatred for the regime to unite behind the government to save the country against an actor that they found even worse than the regime; i.e., Saddam Hussein.
The U.S. is positioning itself in the same vein as Saddam Hussein vis-a-vis the people of Iran. And that cannot be good.
In the end, the people will be willing to sacrifice everything to preserve the regime, because that will become synonymous with the preservation of the country. In the final analysis, the people of Iran are nationalists first, and leave their views of whatever government is in power as a very secondary consideration. This is a fact.
America's recent escapades in the region have been disasters. Afghanistan today is producing record output of opium, and Iranians are suffering under the heavy influence of narcotics brought in from Afghanistan into Iran. Ordinary Iranians blame the U.S. for this; and it is widely known that the year the U.S. invaded Afghanistan (2001), poppy production had fallen to near zero there. Iraq today is fighting the scourge of ISIS in Mosul; the country is divided, and badly broken. The U.S. invasion of Iraq did not lead to a 'better', more 'stable' Iraq. After decades of war, the country is badly broken. Syria too, now has 11 million displaced citizens, 4 million refugees in squalid camps, and 500,000 deaths (and rising), with ISIS being widely connected to the U.S. and its allies (Saudi Arabia, Qatar, Turkey etc.). U.S. involvement in the region has not been value added. Nothing is better today than before the U.S. invasions and U.S.-sponsored actions.
Quite simply, the U.S. has lost regional credibility. Even the threat of war is hollow. After virtually bankrupting the U.S., and spending over 4 trillion dollars, the U.S. has essentially 'lost' the battle in Iraq (to Iran's mullahs). Iraq was or rather 'is' a disaster. Syria was or rather 'is' a disaster. Afghanistan was or rather 'is' a disaster. And Iran is 3x bigger and has 5x the population of these countries! An outright invasion is unimaginable. And the use of proxies like the Kurds and Arabs is not a viable option (look at America's proxy terrorists' ISIS's fate).
Interestingly, the Kurds are U.S. allies too; and likely beneficiaries of U.S. regional involvement -- with a new country carved out of Iran, Syria, Iraq and Turkey. Azerbaijan's dictator is widely seen as a Western puppet, and likely beneficiary of a united Azerbaijan with sections carved out of Iran. And there are other minorities in Iran that have been connected to Western (and Arab) support. So, in effect, ordinary Iranians widely believe that if Iran is attacked it will be splintered into 5 sub-regions. ("Tadjzieh")
To add salt to the wound. Iran has been sanctioned for decades, and Iranians now face travel bans to the U.S. There are no direct relations with the U.S., so Iranians must travel to other countries to even apply for visas, and now this: the travel ban. As if it wasn't hard enough! Why are they being punished? Everyone knows, the regime in Iran was installed by the West? (Look at the pictures of Khomeini landing in Tehran on a French government-financed Air France 747!!)
U.S. actions, rhetoric and alliances are widely seen as resulting in Iran's demise. There is no win-win outcome being proposed here. There is nothing to gain for the people of Iran.