2020 Democratic presidential hopeful Beto O’Rourke on Saturday formally launched his White House bid in his home state of Texas, and used an address in El Paso to focus in particular on the hot topic of immigration.

“If we truly believe we are a country of immigrants and asylum seekers and refugees, the very premise of our strength, success and our security, let us free every single Dreamer from any fear of deportation,” he said, referring to illegal immigrants who entered the country as children.

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O’Rourke, a former congressman who failed to oust Sen. Ted Cruz in the 2018 Texas Senate race, was speaking in his hometown of El Paso just blocks from the U.S.-Mexico border -- one of three rallies in the state. He spoke on a small stage in the city’s downtown, quickly moving through policy issues and pacing from one side to another while surrounded by sign language interpreters.

“This is our moment of truth, and we cannot be found wanting,” he told the crowd. “The challenges before us are the greatest of our lifetimes.”

His speech comes during a week in which Trump has said he is considering shutting the southern border due to Mexico’s alleged inaction to combat the increasing flows of illegal immigrants into the country, and weeks after Trump declared a national emergency at the border to free up more funding for a wall at the border.

Saturday afternoon, Trump used Twitter to urge Mexico to act. "Mexico must use its very strong immigration laws to stop the many thousands of people trying to get into the USA," he tweeted. "Our detention areas are maxed out & we will take no more illegals. Next step is to close the Border! This will also help us with stopping the Drug flow from Mexico!"

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He also criticized Democrats for impeding progress to improve immigration laws, tweeting that "Dems don’t care about the crime, they don’t want any victory for Trump and the Republicans, even if good for USA!"

Democrats have been taking increasingly extreme positions on issues relating to border enforcement -- for instance, advocating the abolition of Immigration and Customs Enforcement (ICE). O'Rourke himself has gone so far as to call for existing barriers to be taken down.

But as his campaign ramped up in El Paso on Saturday, the ex-congressman struck a more bipartisan tone.

In line with his 2018 campaign, O’Rourke said there was a “golden opportunity” for Democrats to work with Republicans on “comprehensive immigration reform” and to “rewrite this country’s immigration laws in our own image, with our own values, and in the best traditions of the United States of America.”

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In his address, he touched on a number of issues, sometimes in rapid-fire succession. Those included more liberal positions such as the federal legalization of pot, combating climate change promising a new Voting Rights Act to “end gerrymandering,” and “high quality universal health care.” In a nod to the city’s large Hispanic population, he spoke in Spanish for the last part of his address.

With a Democratic field that has increasingly embraced left-wing, once-fringe policies, it is far from clear how well O’Rourke’s more centrist political stances that allowed him to stay competitive in the red state of Texas will fare on the national stage.

So far though, initial polls are indicating his support is solid. A recent Quinnipiac University national poll showed O’Rourke in third place among Democrats and Democratic-leaning independents.

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While he formally kicked off his campaign on Saturday, O’Rourke announced his candidacy two weeks ago and attracted large crowds and lots of media buzz as he campaigned in all four of the early voting primary and caucus states. He also raised an eye-popping $6 million in his first 24 hours as a candidate.

O'Rourke was scheduled to speak later Saturday at the historically black Texas Southern University in Houston before an evening event near Austin's state Capitol.

Fox News' Paul Steinhauser and The Associated Press contributed to this report.