President Biden endorsed the U.S. Citizenship Act last week that would create a path to citizenship for most noncriminal illegal immigrants in the United States. Republicans were quick to criticize the bill’s lack of money for border security. But more funds for the border bureaucracy won’t stop illegal immigration. Sadly, however, the better solution—more guest workers—also didn’t make the cut.

The failure to include guest workers violates a campaign promise by Biden. His immigration platform states that his proposed legislation would “expand opportunities for individuals seeking temporary worker visas or another form of legal status for which they may qualify to be able to come to the U.S.” Yet the U.S. Citizenship Act doesn’t address this issue at all.

The relationship between more Mexican guest workers and less illegal immigration from Mexico is as clear as any long‐​term immigration trend in recent American history. In the 1950s and 1960s, the Bracero program funneled hundreds of thousands of Mexican workers into the legal system to U.S. farms every year, and illegal immigration virtually disappeared.

But in 1965, Democrats terminated the Bracero program after unions complained about it, citing now‐​disproven claims that doing so would increase farm wages. By 1970, illegal immigration had spiked again, and many Republicans urged the resurrection of the Bracero program. Indeed, former‐​border state governor Ronald Reagan and presidential candidate repeatedly argued for an open‐​door policy with Mexico.

Once elected, Reagan tried to get more guest workers through Congress, but ultimately, Democrats enacted only an amnesty for long‐​term illegal residents alongside a temporary program that allowed former farm workers to stay or reenter the United States at the southern border and obtain permanent residence. Cross border illegal traffic did fall but then continued at still‐​high, albeit lower rates.

In the 1990s, ramping up the Border Patrol became a bipartisan goal. But without a guest worker program, it had a perverse effect. It became so expensive to cross that anyone who made it in never left, building permanent, albeit illegal, lives here. This caused the illegal population to balloon even as crossings declined.

But then something interesting happened. Permanent lives meant most illegal workers switched to permanent, year‐​round jobs, so suddenly, employers faced a shortage of workers for temporary or seasonal positions. With declining workers coming across the border, employers urged reforms to the seasonal guest worker programs—H‑2A for agriculture and H‑2B for others—that would make those visas more widely available.

In a few years, farmers, landscapers, and other seasonal employers were recruiting tens and then hundreds of thousands of legal H‑2A and H‑2B guest workers from Mexico, and crossings again began to fall even further and faster. Just before the pandemic, illegal immigration had hit a sustained low rate last seen under the Bracero program in the 1960s.

Despite their success, the H‑2 programs have a major shortcoming: they are only for seasonal or temporary jobs. Permanent, year‐​round positions don’t qualify, so employers returned to workers crossing the border. With Mexicans waiting for visas, the new wave of border crossers were from Central America. Rather than evade detection, they crossed, requested asylum, were released, and ultimately received work permits while they waited for a final decision.

The result is hundreds of thousands of Central Americans legally working in the United States in year‐​round jobs as they waited for asylum hearings. But that result came at huge costs to them, their families, and the government. They have to travel illegally through Mexico over a thousand miles, get arrested, and caged often in deplorable conditions just to fill open positions that employers are hiring for.

A better idea would be to allow them to obtain visas to work in year‐​round jobs in the United States and let them fly to the United States. Yet the Biden bill not only lacks this reform. It doesn’t do anything to increase temporary workers at all from anywhere. That’s a huge error with profound long‐​term effects. Biden’s original immigration platform—on which campaigned—explicitly called for more guest workers for Central America. He should return to that plan.