Senate Democrats last week moved to block debate on a bill that would do away with arguably one of the least rational components of the entire U.S. immigration system: the “green-card lottery.” The bill proposes replacing the current diversity-happy, luck-of-the-draw program with one that would give preference in awarding visas to foreign-born graduates of U.S. universities who had earned advanced degrees in science, technology, engineering and mathematics, or STEM.

Senate opponents of the proposal were following the Obama administration’s lead. Days earlier, the White House announced its dissatisfaction with the bill, saying that it did not meet its long-term objectives for comprehensive immigration reform.

To be sure, the STEM Jobs Act is not perfect. Still, it suggests a big step in the right direction toward immigration reform. To understand why, we must understand the program it would replace.

The green-card lottery — known more formally as the Diversity Visa program — was implemented in 1986. Every year, the government offers 55,000 visas to residents of countries with low immigration to the U.S. Applicants need meet only two criteria: They must have a high school diploma, and they must have two years experience in a job that requires at least two years of training. That’s it. From the pool of applicants meeting those criteria, 55,000 names are selected at random and get green cards.

Basically, the controlling criteria for entry is simply “country of origin.” The program, overall, tilts heavily toward low-skilled immigration. The data show that low-skilled immigrants are, in general, far more likely to become a net drain on the public purse than are high-skilled immigrants. Heritage research shows that the typical low-skilled immigrant household takes in $30,160 in benefits, education and services, while paying only about $9,000 into the Treasury.

That doesn’t mean we should admit no one without a postgraduate degree. But it certainly suggests we can do better than merely granting visas based on the luck on the draw.

Rather than perpetuate the flawed and haphazard visa lottery, the STEM Jobs Act would help bring in high-skilled workers in the areas of math, science and engineering. It would require that applicants hold a U.S. doctorate or master’s degree in a STEM field — precisely the kind of workers most needed to meet the growing needs of our 21st century economy. Currently, far too many foreign students educated in the U.S. are forced to return to their home countries upon graduation. It’s a forced “brain-drain.”

A STEM-educated workforce is vital to the security and prosperity of the U.S. Industry increasingly demands highly trained STEM professionals to compete in the global market. And our national security offices increasingly look to science and technology to help stay one step ahead of constantly evolving high-tech threats — from cyberattacks to biochemical assaults. Meanwhile, our visa program blindly shows STEM-educated professionals the door. Think of it as America’s gift to our financial — and perhaps military — competitors.

Ultimately, America needs an immigration and visa policy that (1) works and (2) is responsive to our economic needs. But insisting that “comprehensive” immigration reform must be done in one fell swoop — or not at all — is disingenuous.

Yes, immigration reform should ensure that American companies can get the workers they need; it also should improve border security; it also should enforce workplace and immigration laws and provide real solutions for those now living in the shadows. But it doesn’t have to do it all at once. Congress stands a better chance of developing fair and effective policies that attract bipartisan support if it addresses each of these issues separately.

The STEM Jobs Act seeks to do just that — tackling reform in one discreet area: green-card immigration. It may not be perfect, but blocking debate and refusing to even discuss how to improve the bill is no way to seek and forge consensus

• Jessica Zuckerman is a research associate specializing in homeland security issues at the Heritage Foundation’s Allison Center for Foreign Policy Studies.