Essentially the killing of Mohammadi reinforces the lesson of the October attack that killed dozens of Iran's Revolutionary Guards and several officers in Balochistan. Which is that the US, from Iran's point of view, is no longer deterred from orchestrating or allowing deadly covert attacks on Iran's soil.
Flynt Leverett says it is very unlikely that the US was directly involved in the bombing. He, like many others, hints that, just on the basis of motivation and capability, Israel and/or parties working on Israel's behalf are the most likely suspects.
The problem with accusing Israel is that if US operations extract Iranian scientists and managers of Iran's nuclear program to get information from them, and then US resources build contacts with Iranians who are able to operate in Tehran and the US creates an atmosphere of significant chaos and distrust in Iran that consumes a substantial amount of resources of Iran's security services - and Israel, in that US-created environment, uses information and resources the US has shared with it to choose a target and execute the assassination then this still counts as a joint US/Israeli operation. Even if the US was uninvolved and even unaware of the actual bombing.
On the other hand, just by the nature of the US/Israeli relationship, it is reasonable to believe that information about the attack was presented to the Americans before-hand, and the US could but chose not to veto it.
What is becoming clear is that the late Bush administration took a more serious and firm view towards de-escalating tension with Iran than the Obama administration does. The reason the Bush administration was firmer in restraining Israel than the Obama administration is not that Bush tempermentally favors Iran more than Obama does, but that Bush saw first-hand Iran's capability to regularly cause the deaths of hundreds of US soldiers and Obama has not.
I'm fairly secure that by now Iran is considering ways to recreate the environment that led the Bush administration to seek de-escalation with Iran - which means Iran is now putting into place campaigns, probably in Afghanistan and Iraq, to kill dozens of US soldiers per month. After some time under these conditions, Iran would expect the US to reopen talks.
US interests and Israel's diverge fairly deeply about Iran. Israel considers an Iranian enrichment capability a threat, while the US, outside of its commitment to Israel, does not. Even more broadly, a situation in which US soldiers regularly die in Iraq and Afghanistan while at the same time Iranian nuclear program assets die or are destroyed is more acceptable by Israeli calculations than by American calculations. US interests tend toward de-escalation, Israeli interest tend toward escalation of hostilities between Iran and the US.
As of now, Obama has not been pressed to restrain the Israelis of to tamp down on US' own hostile actions against Iran. Iran likely considers extending agreements reached with Bush into the Obama administration without explicit and verified confirmation from Obama as a mistake that Iran has paid painfully for.
I do not think we will see open war between the US and Iran, but it may be useful to think of now as a new 2006. The US may go for and get modest sanctions against Iran, and Iran will work to establish its ability to cause the deaths of US soldiers in the neighboring countries.
If Iran is actually capable of ramping up violence to the point that it threatens the US conceptions of its missions in the two countries, than the US will return to agreement with Iran, and actually enforce its side of the agreements. I consider it a fairly safe bet that Iran will prove able to increase the rate of US killed in action in both countries this year.
If Iran for some reason proves unable to increase violence in Iraq or Afghanistan, then Obama's gamble would have paid off, and Iran's position with respect to nuclear negotiations will be weakened in some ways. Iran's position will still be stronger in the sense that Iran's domestic stockpile of LEU will be larger than it is now.
The bets have been made on both sides and the dice are rolling. We can only wait to see what numbers turn up.
