The Islamic Republic of Iran is a sponsor of terrorism with global reach. In recent years, it has plotted terrorist attacks not only across the Middle East but also in Thailand, the U.K., France, Greece, Bulgaria, India, and even the United States.

The Iranian government’s ongoing kidnap and assassination plots against U.S.-based dissidents and Trump administration officials have not deterred the Biden administration from continuing its diplomacy with Iran. In recent weeks, Special Envoy Rob Malley has not only met with Iranian diplomats from Iran's U.N. Mission in New York, but diplomats say he now negotiates billion-dollar ransoms for Iranian-American dual citizens held hostage in Iran. The seeming desperation of the White House only convinces both the Islamic Revolutionary Guard Corps and the intelligence ministry that they face no consequences for plots against Americans and America.

Unfortunately, several back doors to the U.S. exist from which Iranian agents might seek advantage. The best publicized, of course, is the porous southern border. This need not mean Iranian agents traveling from Tehran and sneaking across the Rio Grande. In 2010, for example, the Revolutionary Guards sought to contract hitmen from a Mexican cartel to do their dirty work in Washington, D.C.

For Iranian hitmen, some ports of entry are easier than others. Istanbul is a den of espionage and operations, for example, in part because the Turkish government does not require Iranians to receive visas in order to enter the country. Many countries closer to the U.S. are equally porous and negligent. Haiti does not require Iranians to apply for a visa in advance. Granted, an Iranian in Port-au-Prince would stick out like a sore thumb. Dominica, too, allows visa-free travel for Iranians. Like Haiti, it is largely black, but it is a travel destination for a different crowd: The island is home to a number of guest houses, hotels, and resorts for whom a diverse clientele would be normal. Iranians would not appear out of place. The island also has direct flights to Miami and San Juan. Suriname, the former Dutch colony on the Caribbean coast of South America, also has direct flights to the U.S., absent any visa requirement for Iranian citizens.

Among Pacific island nations, Micronesia and Palau, both former U.S. trust territories, also allow Iranians to enter without a visa or to receive a visa on arrival. Both also have flights to Guam, a U.S. territory, or Hawaii. Immigration and Customs Enforcement trains its agents at American ports to detect those who may be criminally suspect. Often this means intercepting concealed food or other contraband. If Iranians can make it to the Caribbean or Pacific with minimal trouble, switching passports or shuttling between islands prior to entering the U.S. or territories such as Guam or Puerto Rico with false documents is relatively easy.

When I studied in Iran, my tutors lamented that, unlike under the shah, they could no longer easily travel the world and explore. Iranians are culturally more cosmopolitan than those around them. For many, Dubai or Doha are escapes, but for some, they want more than shopping or artificial glitz. They will seek out destinations open to them. For regime hitmen, however, such destinations are propped open back doors to exploit.

If the State Department were serious about protecting Americans, it would pressure friendly countries such as Dominica and Palau, both dependent on American tourism, to do the right thing and close the Iranian loophole. If they balk, then it is time to reconsider the wisdom of direct flights to the American mainland or its offshore islands.

Michael Rubin ( @mrubin1971 ) is a contributor to the Washington Examiner's Beltway Confidential. He is a senior fellow at the American Enterprise Institute.