NEW YORK — At a time when the United States should be working more closely than ever with its European allies to combat the growing threat posed by the Islamic State, the U.S. Congress seems determined to go in the opposite direction.

Just days after voting to wash its hands of the Syrian refugee problem even as Europe is struggling to manage an enormous flow, many in Congress are now taking aim at a 30-year-old program that permits visa-free travel between Europe and the United States. In doing so, Congress is jeopardizing U.S.-European cooperation in the fight against terrorism, and could leave the United States more vulnerable to the very attacks that members of Congress say they want to prevent.

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The so-called Visa Waiver Program (VWP), signed into law by President Ronald Reagan in 1986, permits citizens of Western Europe and other friendly nations to travel to the United States without the expense and time involved in obtaining a visa. The idea was to boost travel and tourism, and it has been an enormous success. Some 40 percent of all overseas visitors, about 20 million annually, come from VWP countries.

But in the wake of the 9/11 attacks, both Congress and the George W. Bush administration rightly grew concerned that the program was vulnerable to exploitation by terrorists. While all 19 of the hijackers came from countries where visas were required — most from Saudi Arabia — two cases demonstrated that some risks were posed by VWP. Zacarias Moussaoui, alleged to have been the intended 20th hijacker, was a French citizen, and Richard Reid, the so-called shoe bomber who tried to detonate an explosive on a December 2001 trans-Atlantic flight, held a British passport. Democratic Senator Dianne Feinstein of California wanted to shut down the program after 9/11, and she is again leading the push for new legislation in the wake of the Paris terror attacks, arguing that the VWP remains “the soft underbelly of our national security policies.”

While that charge held some truth a decade ago, it is wholly false today. Instead, the VWP is a shining example of how U.S. cooperation with allies is a much better strategy for securing the homeland than going it alone. The 9/11 Commission, which examined in detail the challenges of stopping terrorist travel, concluded that “the U.S. government cannot meet its own obligations to the American people to prevent the entry of terrorists without a major effort to collaborate with other governments.”

This is exactly what happened with the VWP after 9/11. Recognizing their common interest in stopping terrorists while encouraging lawful travel, the United States and Europe worked closely together to remake the VWP. Indeed, Stewart Baker, who was general counsel of the National Security Agency and assistant secretary for policy at the Department of Homeland Security during the Bush administration, has argued that the VWP “provides unmatched benefits to U.S. law enforcement and security interests.”

Here’s why. In most countries where visas are required, the United States is on its own in assessing the risks that any individual traveler poses. State Department consular officers have access to terrorist watch lists and criminal databases, and take fingerprints to confirm identity, but otherwise often know little or nothing about the would-be travelers. Interviews are required, but they are usually brief and not terribly revealing.

For the typical European traveler to the United States, the process today is actually more rigorous.

First, any country that is part of the VWP is required to share all of its terrorism-related intelligence with the United States. The United States is much more likely to identify a potentially dangerous European traveler as a result of intelligence provided by European law enforcement than by requiring a five-minute visa interview.

Secondly, the VWP mandates that all members issue machine-readable, biometrically enhanced passports, and that they share immediately all data on lost or stolen passports. As a result, the likelihood of anyone entering the United States on a fraudulent European passport is extremely low.

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Finally, the idea that the VWP is “visa-free travel” is something of a misnomer.

A French citizen is not permitted, as the notion would suggest, to arrive at Charles de Gaulle airport in Paris, buy a ticket, and hop on a plane to New York. Any would-be traveler has to register in advance with the U.S. government through what is known as the Electronic System for Travel Authorization (ESTA). They are required to provide a complete history, including biographic information and past criminal convictions or visa revocations. Their identities are checked against multiple watch lists and against lost and stolen passport data. If there is even the slightest suspicion, the U.S. government can reject the application and require the traveler to undergo a visa interview.

Since August, 2008, more than 4,000 travelers have been blocked because of hits against terrorism databases, and another 22,000 for using lost or stolen passports. In short, the screening process is in some ways more thorough — and certainly backed by more robust information — than the screening process for visa applicants.

This is not to say there is no room for improvement. There is certainly a genuine danger posed by some first or second-generation immigrants holding European passports. Those who have traveled to war zones like Syria or Iraq are clearly deserving of extra scrutiny. But the Obama administration figured this out long before the U.S. Congress did. More than a year ago, DHS Secretary Jeh Johnson announced several enhancements to ESTA designed to help identify ISIL terrorists carrying European passports. Further steps, such as speeding up the requirement to use biometric passports rather than allowing older ones to be phased out, would be warranted.

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The danger of congressional action to pare back the VWP — even a seemingly modest step such as requiring visas of any European who has traveled recently to Iraq or Syria — is that it would weaken the cooperation that has made the program such a success. Europe would likely resent any of its citizens being singled out in statute for special treatment. A far better approach would be to help Europe strengthen its own border security and entry procedures, so that better intelligence can be gathered on European citizens who are traveling to conflict zones.

The United States cannot stop terrorist travel on its own. Whatever Congress may wish, no mixture of bans, pauses or new unilateral screening requirements will increase American security. Instead, the United States needs to bolster intelligence sharing and cooperate with its allies at the deepest levels to help identify and stop those individuals who pose genuine security threats — not just to the United States but to Europe as well.

Edward Alden is a senior fellow at the Council on Foreign Relations and the author of “The Closing of the American Border: Terrorism, Immigration and Security since 9/11” (Harper Collins, 2008).