Rights groups and legal experts have slammed US President Donald Trump's call to end the Diversity Visa Program after Tuesday's attack in New York City, saying his remarks are "rash" and a "vast overreaction".

Trump called for the end of the programme, which awards green cards to about 50,000 people every year, after Uzbek national Sayfullo Saipov allegedly drove a rented truck down a crowded bike path in New York, killing eight people and injuring at least a dozen others.

"The terrorist came into our country through what is called the 'Diversity Visa Lottery Program'", Trump tweeted on Wednesday, adding that he wants a "merit based" programme instead.

A day later he said he was calling on Congress to "terminate" the programme, saying its "applicants are randomly selected in a random lottery and the people put in that lottery are not that country's finest."

But immigration rights groups and legal experts say labelling the programme as a strict lottery is "misleading", and punishing millions for the actions of one individual is "insane".

What is the Diversity Visa Programme?

Congress created the Diversity Visa Program under the 1990 Immigration Reform Act to aid populations that were underrepresented among US immigrants, Antonio Meloni, executive director of Immigration Advocacy Services, told Al Jazeera.

Aimed initially at increasing the immigration of Irish nationals, immigrants of European origin were the primary recipients of diversity visas. Gradually this has shifted to those of African origin, who receive, on average, 40 percent of available visas, according to a Congressional Research Service study in 2011. Only those from eligible countries - those that have sent less than 50,000 immigrants in the past five years - are able to apply.

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In some years up to 16 million people have applied for the programme. About 100,000 applicants are selected from this pool, but only half will ultimately receive green cards, according to Meloni.

He added that the process of applying is more complex than the first step - filing an online application - would suggest.

"It's not as if you win the lottery and you come in," Meloni said.

Individuals applying this year during the one-month application period from October 18 to November 22 must provide documentation showing they have completed 12 years of education or two years of work.

This may not seem like much, Anu Joshi, director of immigration policy at the New York Immigration Coalition, said, "but for a lot of people in other parts of the world, it's not that easy to prove, to get all of the documents".

"Winning" the lottery is no guarantee. Those selected must then apply during the second year for a visa and begin the same marathon of vetting procedures, including background checks and medical examinations all residency applicants undergo. Only 7 percent of recipients can come from any one state, further limiting the chances of those from countries with large applicant pools, according to Meloni.

In regards to the risks to national security, Joshi told Al Jazeera that calling the diversity visa process a "lottery" is "misleading".

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"Sure, diversity applicants throw their names into this pool, and if they get selected, that's the lottery part," Joshi said.

"After that, everything is the same as anyone else who is trying to emigrate to the United States … They face all of the same barriers in terms of national security threats."

It is typically not until the third year that candidates are interviewed by the US Department of State or consulates before their visas can be issued, Meloni added.

Who applies for the Diversity Visa Program?

Since its founding, well over one million immigrants have been admitted to the US through the diversity visa programme, Meloni said.

Applicants from around the world, whether applying alone or with their families, do so with the same aim: To try to make a better life for themselves and their families, according to rights groups.

The majority of residency visas are granted on the basis of family ties, Fred Tsao, senior policy counsel at the Illinois Coalition for Immigrant and Refugee Rights, told Al Jazeera.

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As a result, the diversity visa is "a gated pathway to the United States that they might not otherwise have", Tsao said.

Other legal pathways to US immigration are through employment, asylum or refugee resettlement, which are difficult to attain and time-intensive. The diversity visa lottery remains the most desirable prospect, particularly for immigrants from Africa or Asia, Tsao explained.

A third of immigrants from Africa come to the US with a diversity visa, according to the US Department of State.

While the programme may not take the form Trump imagines for a merit-based system, Amaha Kassa, founder and executive director of African Communities Together, told Al Jazeera that he believes the "stringent requirements" and challenge of navigating the process of the diversity visa process "select for higher-educated people".

African immigrants, who enter the country through a variety of ways, have higher educational achievement than both the overall immigrant and overall US populations, according to a Pew study of census data from 2013.

Diversity visa recipients also have less than half the unemployment rate of other green card holders, and more than twice as many are employed in professional or managerial positions, a 2011 Congressional Research Service report found.

'Won't stand by'

President Trump's recent call to end the diversity visa lottery is not the first time the programme has been challenged since it was implemented.

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The 2011 study by the Congressional Research Service addressed concerns that the programme was vulnerable to fraud and the difficulty of conducting background checks in some of the countries where applicants live. In 2013, a bill that would have terminated the programme passed in the US Senate, but was ultimately rejected in the House of Representatives.

Earlier this year, Republican Senator Tom Cotton of Arkansas introduced the RAISE Act, which would save the Deferred Action for Childhood Arrivals, or DACA, policy, but at the expense of the visa lottery programme.

Cotton argued in August that cutting immigration in half and prioritising highly-skilled immigrants would "spur economic growth and raise working Americans' wages".

Immigrant community organisations are not standing idly by, Kassa told Al Jazeera.

"My organisation and other African community organisations, we would and we will oppose any bill - such as the RAISE Act - that would eliminate the diversity lottery," Kassa said.

Trump, however, continues to advocate for redirecting immigration policy to focus on merit-based visas as a measure to improve domestic security.

The response has led to heightened concerns among recipients of diversity visas, who feel villainised despite having followed procedure to enter the US legally, Kassa said.

Immigration Advocacy Services' Meloni told Al Jazeera that the inclusion of a merit-based system would not be a detriment, but also would be no replacement for the diversification provided by the lottery programme.

Whatever path immigration reform takes, Kassa told Al Jazeera, it should not be undertaken rashly or in reaction to an isolated tragedy.

"We're now reacting to one out of those over a million people who were admitted through this programme. Our view is that we should be making policy based on the million, not based on the one," Kassa said.