A persistent threat scenario against the U.S. has been foreign terrorist organizations—acting independently or in cooperation with violent transnational criminal organizations, and perhaps backed by anti-American regimes in the region—launching a terrorist attack from across our southern border.

It is a scenario the Obama Administration has recognized but generally minimized. For example, the U.S. State Department’s 2010 Country Reports on Terrorism reported:

The threat of a transnational terrorist attack remained low for most countries in the Western Hemisphere. There were no known operational cells of either al-Qa’ida- or Hizballah-related groups in the hemisphere, although ideological sympathizers in South America and the Caribbean continued to provide financial and moral support to these and other terrorist groups in the Middle East and South Asia.

The continued unfolding of the Iran plot to assassinate the Saudi ambassador in the U.S. is also a reason to revisit the terror threat in the Americas. In the indictment and yesterday’s press conference, it became clear that co-defendant Manssor Arbabsiar, a naturalized Iranian living in Texas, traveled repeatedly to Mexico in search of hired assassins willing to work for Iranian payoffs.

There Arbabsiar thought he was enlisting the services of Mexico’s deadliest, most ruthless criminal organization, the Zetas, to carry out the contract assassination in exchange for $1.5 million in Iranian cash. The Zetas, with their paramilitary tactics and ruthless disregard for human life, would make a perfect fit with terror-minded Iranians.

Little wonder Tehran would seek to enlist them as hired executioners to conduct assassinations and wreak havoc in Washington, D.C.

The uncovering of the Iran plot is a wake-up call here in the U.S. but also in the Western Hemisphere. It compels us take an even tougher stance against those who eagerly embrace Iran and act as an Iranian conduit into the Western Hemisphere. Hugo Chavez’s Venezuela—followed by nations like Bolivia, Ecuador, Nicaragua, and Cuba—certainly head the list and require ever-increasing scrutiny.

The growing Hezbollah threat has been well-documented by Ambassador Roger F. Noriega and Jose R. Cardenas in “The Mounting Hezbollah Threat in Latin America” and by investigative journalist Douglas Farah. Hezbollah works closely with Iran’s Revolutionary Guard and Qods Force, whose operative, Gholam Shakuri, was indicted along with Arbabsiar in the plot.

U.S. law enforcement is to be applauded for foiling yet another terrorist plot. The Obama Administration should now follow up the unraveling of the conspiracy with strong international actions against Iran. In the Western Hemisphere, Iran’s allies—who open their doors to Iranian intelligence and terror operatives—should also feel more U.S. and international heat.