President Trump is promoting comprehensive immigration legislation drafted by key House Republicans that touches on all aspects of the system. The bill would provide legal status to young immigrants, cut legal immigration, and provide for more border agents, but one provision should not be ignored: a biometric exit system. It’s a big waste of money, and Congress should resist efforts to fund it.

Biometric exit’s logistics are difficult

Current law requires the Department of Homeland Security (DHS) to collect a biometric identifier—in practice, fingerprints and digital photos—from foreign visitors entering and leaving the United States. In theory, this system would allow them to identify individuals who overstay their temporary visas. After 9/11, DHS implemented the entry half, but it still has not rolled out a system for those exiting.

The biometric entry system—known as US-VISIT—was relatively easy to implement because foreign visitors to the United States already underwent screening at ports of entry, and as a security tool, it made sense. It allows DHS to confirm that a person trying to enter is the same person who applied for a visa overseas, which undermined visa fraud and the use of aliases in the visa entry process.

The biometric exit system has no similarly easy path to implementation. Airports are not set up to screen travelers exiting the United States. As the Government Accountability Office (GAO) has found, “airports generally do not have designated and secure exit areas for conducting outbound immigration inspections, nor are there checkpoints for travelers to pass through where their departure is recorded by a U.S. immigration officer.”

At land ports of entry, the situation is even more hopeless. GAO found that “many land POEs do not have sufficient space to deploy equipment and staff.” Moreover, a biometric exit system would require motorists to stop and physically leave their vehicles. GAO notes that this “would cause extensive delays.” DHS did test biometric exit kiosks for pedestrian traffic, but these failed because agents had to spend too much time helping people and desert conditions damaged the equipment.

Biometric exit is an unnecessary expense

Nor does biometric exit have the same benefits. DHS already tracks most overstays using airline flight manifests. Airlines send DHS the names of anyone who has boarded an outbound flight, and DHS compares this information against US-VISIT entry information. In 2016, this flight manifest system identified 544,676 people as having overstayed and not left the country—1 percent of all air and sea entries.

While some share of these people—mainly Canadians and Mexicans—may have left through ports of entry, this system identifies a massive pool of people who DHS could target for removal operations, but they don’t. DHS spends only 2 percent of its time investigating overstays. Of the nearly 700,000 foreign visitors that DHS has identified as overstays from 2004 to 2012, it arrested only 9,000 (1.2 percent).

Expanding an exit system to land ports of entry would only add to the massive stack of uninvestigated visa overstays. Biometric exit without much more aggressive interior enforcement serves little purpose, while coming at a great cost. The Senate Judiciary Committee in 2013 obtained an estimate from DHS that full biometric exit would cost $25 billion—airports would cost $6.4 billion alone.

This only includes the cost to the government. It ignores costs to travelers and businesses who are delayed leaving the country. Delays entering the United States along the southern border already cost the U.S. economy billions—more than $6 billion in California alone. Congress should work first to reduce these delays that have serious negative impacts on the economy before imposing an expensive system with a dubious purpose.

Overstay crackdown isn’t worth it

Some might argue that the biometric exit would be valuable if DHS simply spent more time targeting overstays. But the department’s priorities make sense. Every visitor to the United States receives thorough vetting before entry, while people who cross the border do not. Thus, starting with border crossers is logical from a security perspective.

Overstay investigations are exceptionally labor intensive for low priority offenders. Consider that of the 44,500 overstay leads that DHS investigated from 2004 to 2012, it arrested just 9,000, mainly because nearly half ended up leaving the country or adjusting to a legal status before an apprehension was made. Another quarter were never located. This is a huge investment for few arrests.

By contrast, DHS currently apprehends illegal immigrants—including some overstays—mainly after states and localities arrest them for local crimes. Prioritizing overstays would mean passing on people who 1) are guaranteed arrests and 2) are alleged to have committed some other violation of law beyond immigration offense. To target both overstays and those arrested by local police would require far more resources than Congress currently spends on enforcement. Even then, it’s not clear that overstays would be DHS’s priority. There are criminal fugitives who could be tracked down.

Biometric exit is a costly enforcement hammer without any nails to strike. DHS is already well aware of many visa overstays, but prioritizing them would mean ignoring higher priority and easier arrests. Without dramatic reductions in the illegal population, a crackdown on visa overstays will never make much sense, making biometric exit almost entirely superfluous.