In 2011, the US stopped an attempt by agents of the Iranian Quds Force (it is debated wether they were sanctioned by the Iranian government or if they were rouge) to commit terrorist attacks on US soil.
The Iranians allegedly planned to hire a Mexican drug cartel to assassinate the Saudi ambassador to the United States by bombing restaurant in Washington, DC that the ambassador frequented. The Iranians also asked for the bombing of the Saudi and Israeli embassies in DC. It is almost certain that a large number of American civilians would have died in the attacks. Fortunately, the Iranians in question wound up contacting a DEA agent posing as a representative of a drug cartel, and the plot was foiled.
What if the Iranians had been successful in carrying out these attacks? How would the Obama administration have responded? Would they have been willing to go to war with Iran? How would the 2012 election have been effected?