Former congressman Beto O’Rourke officially kicked off his presidential campaign Saturday with a plea for unity and compassion for Americans struggling to better themselves and migrants seeking relief at the U.S.-Mexico border, just blocks away from where he stood.

“Whatever our differences — where you live, who you love, to whom you pray, for whom you voted in the last election — let those differences not define us or divide us at this moment,” he told several thousand supporters who gathered in his hometown’s historic downtown for the first of three kickoff rallies in Texas on Saturday. “Before we are anything else, we are Americans first.”

O’Rourke was critical of President Trump, who he cast as using “fear and division” to corral political support, but most of his address appealed to American virtues.

“We will not allow ourselves to be defined by our fears or our differences,” he said, but rather “our aspirations, our ambitions.”

O’Rourke was close to the Paso del Norte International Bridge, under which Border Patrol agents have detained hundreds of migrants, including families with young children, in a temporary tent setup because a dramatic influx of asylum seekers has filled the processing facilities.

“They are our fellow human beings,” O’Rourke said, “and deserve to be treated like our fellow human beings.”

Beto O’Rourke appears in El Paso on Saturday. (Sergio Flores/For The Washington Post)

O’Rourke called for aid to Central American countries to stem the flow of needy people, for protections for “dreamers” brought to this country as young children and for a path to citizenship for millions of undocumented people already here. He scorned the president’s border crackdown, particularly its impact on women and children.

“Let’s make sure we never take another child from another mother at their most desperate moment,” said O’Rourke, who during his speech spoke for several minutes in Spanish.

At a time when Trump has declared border security one of the biggest challenges facing the United States and has made the fight for a wall a centerpiece of his presidency, O’Rourke offers a vastly different and far more positive view of the border and of the migrants trying to cross it.

O’Rourke’s campaign estimated that at least 6,000 packed into a downtown intersection for the rally, a crowd that included many El Paso residents, including several who bragged about having met O’Rourke long ago, and supporters who traveled from places like New Mexico, Arizona and Los Angeles.

Thousands more O’Rourke supporters scattered across the country watched his remarks at parties held in living rooms, a college lecture hall in South Carolina, a musical instrument store in Oklahoma City, a hair salon in Tennessee, a rooftop in Brooklyn and a bar in Cedar Rapids, Iowa. The campaign proudly boasted that supporters had organized watch parties in all 50 states, including one gathering in North Dakota and two in Hawaii.

O’Rourke meets supporters and poses for photos after his El Paso speech. (Sergio Flores/For The Washington Post)

O’Rourke has said that he wants to run “the largest grass-roots campaign this country has ever seen,” and he has turned away donations from political action committees. During his first two weeks of campaigning, O’Rourke attended dozens of events in eight states, usually in small, intimate spaces like coffeehouses and taquerias where voters could shake his hand and ask questions. During the first 24 hours of his campaign, O’Rourke hauled in $6.1 million, the most reported in that period for any candidate.

O’Rourke built a national following during his unsuccessful Senate race last year, but now that he faces fellow Democrats, his voting record in Congress and policy stances — or, sometimes, the lack of them — have come under heightened scrutiny.

His ideological position across the sprawling field of candidates for the Democratic nomination is still unclear. Several candidates, including Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (Mass.), are seen as more liberal than O’Rourke, while Sen. Amy Klobuchar (Minn.) has focused on such issues as infrastructure that could appeal to more moderate or conservative voters.

On Saturday, O’Rourke shared many of his broad goals for the country: Establishing a universal health-care system, increasing pay for public school teachers, investing in rural areas, strengthening unions, equalizing pay rates, combating climate change, ending gerrymandering and ensuring that all veterans have a place to live. He also reiterated his desire to reform the criminal justice system by legalizing marijuana and expunging the records of those once caught with it, along with getting rid of for-profit prisons and cash bail.

But his resounding message was a promise to unite the country — an idea that often felt lofty, especially as a small group of pro-Trump protesters gathered nearby and booed.

“Everyone can see it,” said Art Carreon, 52, who works for a local school district, referring to the division in the country. “It’s like a cancer that grows and grows and grows, like you just can’t get rid of it.”

But Carreon is hopeful that the division could quickly end under the right leadership: “We just need one spark.”

While O’Rourke favored a do-it-himself approach in his Senate candidacy and in the early days of the presidential effort, he has moved recently to professionalize the campaign. In picking a campaign manager, O’Rourke passed over those who worked on his Texas races and hired Jen O’Malley Dillon, a veteran organizer and data expert who was the deputy campaign manager for former president Barack Obama’s reelection campaign.

But O’Rourke wants the campaign to maintain the look and feel of a scrappy effort fueled by grass-roots activists — which is why he formally kicked it off Saturday not in a stadium or an arena, like the venues Trump books for his rallies, but in the streets of El Paso.

Just before O’Rourke took the stage, staffers removed a lectern so that the candidate could roam as he spoke. The stage was set in the center of the crowd so for those who watched on television, the candidate seemed to float amid his cheering fans. In his closing message, he told them: “The power of people is what is necessary for us to accomplish our priorities.”

Afterward, as rock music blared, O’Rourke and his family exited the stage via a barricaded walkway — but he and his wife soon left its safety to join the crowd, thank people and pose for selfies. He had a commercial flight to catch to his next rally, scheduled for Saturday afternoon in Houston, but he lingered for more than 20 minutes.

“Mr. President!” one woman shouted out to him. A man yelled: “Our next POTUS!” Another woman yelled at the crush of people to be careful or someone might get hurt, as a young man marveled: “It’s crazy. It’s like a mosh pit in there.”

“He’s right here in it. It’s about time that we have somebody that is like that,” said Delia Snyder, 53, an educator from El Paso who owns a veterinary clinic with her husband. “He’s got the charisma, he’s got the heart. He’s really down with the people.”