Democratic presidential candidate Joe Biden, unveiling his immigration policy outline ahead of the first 2020 debates, is calling for US Congress to grant citizenship immediately to more than 800,000 US residents who were brought to the country illegally as children.

The former vice president and current leader in the polls to win the nomination unveiled some of his immigration priorities on Monday in a newspaper op-ed that blisters President Donald Trump for an “assault on the dignity” of the Latino community through policies and rhetoric designed to “scare voters” in 2020.

“Trump repeatedly invokes racist invective to describe anyone south of the Rio Grande,” Mr Biden wrote, noting “horrifying scenes … of kids being kept in cages” and other “actions that subvert our American values and our ability to lead on the global stage”.

Mr Biden, who launched his 2020 campaign in April, calls for streamlining the asylum system for migrants and spending more on electronic security at US borders rather than Mr Trump’s proposed US-Mexico border wall.

Mr Biden pledges an overhaul of US foreign policy in the Americas, echoing fellow Democrats who have blasted Mr Trump’s approach to Mexico, Central America and South America.

“The Administration’s Latin America policy is at best a Cold War-era retread, and at worst an ineffective mess,” Mr Biden wrote.

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President Donald Trump has made border security his signature policy (Andrew Harnik/AP)

The op-ed is published in the Miami Herald and El Nuevo Herald, with Mr Biden using the English and Spanish versions to praise the diversity of the surrounding city where 20 Democratic candidates will take the debate stage in two heats on Wednesday and Thursday.

Other than the so-called Dreamers brought to the US as children, Mr Biden’s outline does not directly address the more than 11 million immigrants in the country illegally.

But as vice president in President Barack Obama’s administration, he backed a comprehensive immigration overhaul that would have established a path to citizenship for most of those residents.

That effort cleared the Senate but died in what was then a Republican-led House.

Mr Trump has said his hard-line immigration policies are necessary to keep the country safe.

The immigrants brought to the US as children are commonly referred to as Dreamers because of never-passed proposals in Congress called the Dream Act, which would have allowed them to remain in the country if they met certain criteria.

Opponents say the act would reward people for breaking the law, encourage illegal immigration and hurt American workers.