According to Director of National Intelligence James Clapper, the plot “shows that some Iranian officials — probably including Supreme Leader Ali Khamenei — have changed their calculus and are now more willing to conduct an attack in the United States in response to real or perceived U.S. actions that threaten the regime.”

This new calculus, intelligence officials believe, dates back to January 2010, when the Quds Force decided that it and Hezbollah, its primary terrorist proxy, would embark on a new campaign of violence targeting not only Israel but U.S. and other Western targets as well.

In the wake of last July’s attack on Israeli tourists in the Bulgarian city of Burgas, a barrage of journalists called asking me to explain the logic of the attack. I was finishing a book on Hezbollah — Hezbollah: The Global Footprint of Lebanon’s Party of God, due out next year — but still could not easily place the attack within Hezbollah’s established modus operandi. The more I thought about it, the more perplexed I became. So, much to my editor’s dismay, I stepped away from my keyboard long enough to meet with diplomats and intelligence and military officials from several countries to try and make sense of the new trend of Shia extremist attacks tied to Iran and its proxies. Here is what I have come to understand.