With so many immigrants crossing the border illegally, Congress is overlooking another growing crisis in America’s legal immigration system. The central finding of a new study this week from the Cato Institute shows that legal immigrants are waiting longer than ever before for the chance to apply for green cards. If Congress wants immigrants to follow legal pathways, it should start by fixing the ones that already exist.

These waits were not caused by bureaucratic delays in processing applications and petitions. Rather, the increasing delay is a result of the arbitrary annual limits on green cards that Congress last created in 1990 — 226,000 for close relatives of citizens and legal permanent residents, and 140,000 for workers and investors (as well as their spouses and minor children).

Even as the U.S. population has grown by a third and the economy has doubled in size, these limits have been static. If the numbers run out during the year, immigrants must wait. This disconnect between a dynamic society and static immigration limits forces legal immigrants to wait longer and longer for the chance to apply for their green cards, as legal permanent residence is known.

In the three decades since the last reform, the average time that it took a legal immigrant to get to the front of the lines doubled from two years and 10 months to five years and eight months, according to a new analysis from the Cato Institute. The average disguises huge variation in the wait times because each line moves at different speeds. More than 100,000 legal immigrants (28% of the quotas) waited at least a decade — in some cases, two decades — to apply for a green card.

Contrast that with 1991, when current quotas went into effect: Just 3% waited a decade or more. Back then, nearly a third had no wait at all because of the quotas. By 2018, the share with no wait had fallen to just 2%.

But here’s the thing: It’s about to get much worse for legal immigrants. The waits have caused a massive backlog of nearly 5 million immigrants waiting behind those who applied for their green cards last year. In some categories, that means that new applicants will face astronomical waits of a half century or more if everyone sticks it out.

For example, it would take about a century to process all married adult children of U.S. citizens from Mexico. Obviously, that will never happen; 40% of those children will die before they can apply for a green card. Altogether, the new study projects that 675,000 would-be legal immigrants will die waiting if everyone refuses to give up on the process. That’s 14% of the backlog in 2018.

These waits are not in the national interest. Forcing legal immigrants to wait this long forces foreign talent to head for other countries, as one recent paper from the National Bureau of Economic Research found. Immigrant workers from India wait the longest despite the fact that they have the highest wage offers. The waits also cost the U.S. tens of billions of dollars in foreign direct investment each year.

This policy not only separates U.S. citizens from their adult children and siblings, but also keeps out legal immigrants who, contrary to perceptions, are more skilled than the U.S. population. Ultimately, the arbitrary quotas suppress the U.S. immigration rate, which, as a share of its population, already ranks in the bottom third of wealthy nations.

With more job openings than job seekers, the U.S. needs immigrants to grow its economy. President Donald Trump is right to want those immigrants to come legally, but most immigrants don’t have an option for legal immigration. They don’t have a U.S. citizen family member or a college degree and employer willing to spend thousands of dollars in fees to hire them.

The U.S. desperately needs new pathways for immigrants to enter legally, but if Congress moves to add categories, it should fix the ones that it already has. As the economy grows, the number of foreign workers made available to employers should grow. As the number of households grows, the number of family sponsorship slots should expand.

David Bier is an immigration policy analyst at the Cato Institute. He wrote this article for the Washington Post.