EL PASO, Texas (Reuters) - Democratic presidential candidate Beto O’Rourke held a major rally in El Paso, Texas, on Saturday, a city thrust to the center of America’s immigration debate by President Donald Trump and the U.S government this week.

O’Rourke, a former congressman from El Paso, kicked off a series of three rallies in Texas in his bid to become the Democratic nominee a day after Republican Trump threatened to close the U.S. border with Mexico as soon as next week.

Speaking in El Paso, a few hundred yards from the border with Mexico, O’Rourke decried the Trump administration’s immigration policies and the president’s call for a border wall.

“We’ll find security not through walls,” he declared to cheers from several hundred supporters as he officially launched his presidential campaign.

Before switching to Spanish to finish his speech, O’Rourke denounced what he called Trump’s policies of “fear and division” and accused the president of seeking “to keep us apart and to make us afraid of one another.”

“Let’s remember, every single one of us are fellow human beings and deserve to be treated like fellow human beings,” he said.

O’Rourke’s rally in El Paso was long-planned, but the city became central to America’s immigration debate this week.

Slideshow ( 19 images )

U.S. Customs and Border Protection Commissioner Kevin K. McAleenan told reporters in El Paso on Wednesday the southern border system was at breaking point because of the number of illegal immigrants crossing the border each day.

Trump, who is still determined to build a barrier along parts of the southern border, said on Friday: “There’s a very good likelihood that I’ll be closing the border next week, and that will be just fine with me.”

Trump has repeatedly said he would close the U.S. border with Mexico during his two years in office. His latest threat had workers and students who frequently cross the border worried about the potential disruption to their lives.

Trump and O’Rourke held dueling rallies in February in El Paso, which is already divided from Mexico by steel fencing.

Trump wants it reinforced and hundreds of miles of additional fencing built along the border. O’Rourke opposes any new border structures and opposition to Trump’s border wall and immigration policies has been a centerpiece of his campaign.

“We are safe not despite the fact we are a city of immigrants and asylum seekers - we are safe because we are a city of immigrants and asylum seekers,” O’Rourke said in El Paso on Saturday.

Slideshow ( 19 images )

O’Rourke, who announced his White House campaign on March 14, shot to national prominence last year in an unexpectedly close race against incumbent Texas Republican Senator Ted Cruz.

His Texas rallies will be watched via livestream at more than 1,000 locations across America, according to his campaign.

More than a dozen contenders are fighting to become the Democratic Party’s candidate to take on Trump in 2020.

The O’Rourke campaign sent multiple requests to potential supporters for campaign donations before his rallies in El Paso, Houston and Austin on Saturday, a common practice among presidential hopefuls. The messages stressed the importance of donating before Sunday, the deadline for first quarter fundraising reports with the Federal Election Commission.

O’Rourke, 46, smashed fundraising records as a Senate candidate and raised $6.1 million in the first 24 hours of his presidential campaign, the largest first-day haul of any announced candidate this year.

However, he has struggled to see a strong campaign work ethic translate into a significant boost in early polling.

O’Rourke trails former Vice President Joe Biden and Vermont Senator Bernie Sanders by double digits, according to early polls among Democratic voters. Analysts warn that polls this early, before the first nominating votes are cast in Iowa in February 2020, are unreliable.

Biden has yet to join the race, although he is expected to announce his presidential candidacy soon.