PHILADELPHIA -- In the nearly two and half years of President Donald Trump's administration, immigration has been both a cornerstone of his administration and election efforts. It's also been a unifying force for Democrats, with the 24 candidates seeking to oust him showing near-universal alignment as they condemn the president's hardline approach on the campaign trail.
This weekend, ahead of the Immigration and Customs Enforcement's expected raids in 10 major cities, targeting thousands of undocumented immigrants -- as outlined by Trump -- four 2020 Democrats channeled the anger and stress over the White House's broader immigration agenda before a crowd of nearly 4,000 activists comprising the left flank of the Democratic party, according to event organizers, at the NetRoots Nation annual convention.
On Saturday, in the Philadelphia Convention Center, Sen. Elizabeth Warren, D-Mass., called the treatment of immigrants in U.S. custody "abuse;" former Housing and Urban Development Secretary Julián Castro asserted that the administration must think Americans are "stupid;" Sen. Kirsten Gillibrand, D-N.Y., called the raids "disgusting;" and Washington Gov. Jay Inslee said he was "morally shocked" after Vice President Mike Pence's visit to a border detention facility in McAllen, Texas on Friday.
"To anyone who's working in this system, understand you abuse immigrants, you physically abuse immigrants, you sexually abuse immigrants, you fail to get the medical care that they need, you break the law of the United States of America and Donald Trump may be willing to look the other way, but President Elizabeth Warren will not," Warren said on stage. "On my first day, I will empower a commission in the Department of Justice to investigate crimes committed by the United States against immigrants."
In a room that was largely home turf for Warren -- the audience greeted her on stage with chants of "Warren" as they stood on their feet -- she was the only candidate to be interrupted throughout the nearly four-hour forum by a group of protesters who sought to turn the conversation to immigration while holding a sign that read, "legalize 11 million/reunify all families."
A couple of attendees in the audience defended the senator during the brief interruption, shouting at the protesters "we're all with you" and "we're on your team."
But then Warren addressed the protesters directly, agreeing with them as she said, "Let's talk about immigration."
Earlier this week, she unveiled her immigration platform which calls for, among other things, the decriminalization of unauthorized border crossings; a stance crowned by fellow candidate Castro.
In the early phases of the Democratic primary, the same progressive wing that elevated the 2016 presidential campaign of Sen. Bernie Sanders, I-Vt., who was notably absent from the lineup after being heckled by Black Lives Matter activists at the 2015 event, continues to pull the massive field of candidates and the party to the left. But as the 2020 Democrats explore their differences on a host of issues on the trail, before the impassioned liberal audience, they toed the line of the progressive movement, with immigration at the forefront of the conversation.
Seeking to win over the leftist crowd, the presidential hopefuls spouted harsh words against the president over the politically fraught issue of immigration and pitched similar agendas on the topic during back-to-back appearances at the forum.
"[Trump is] betting basically, that there are enough Americans out there, whose fear and paranoia can be stoked in a way that they're going to go out and vote for him," Castro said Saturday. "And what I'm betting with my immigration plan is that there are enough Americans, whether they're white or black or Latino or Asian American, Native American, whether they're rich or poor, whether they live in a big city or a small town, that are going to respond to common sense and compassion, instead of cruelty. That those values of respect and basic humanity are stronger than his fear and paranoia. And so that's what I would use if I'm president United States."
After his Q&A on stage, the former Obama-era cabinet secretary, who has centralized his campaign on immigration reform, spoke with reporters on the sidelines of the event, and said of Pence's trip to Texas, "This administration must think that people are stupid, that they can't see what they see with their own eyes. I'm going to believe what I see with my own eyes. Not what Donald Trump says with his lying mouth. And I think a lot of Americans feel like that."
"What happened yesterday, was that what the vice president thought was going to be a neat little photo opp for him and his colleagues turned into a photo op nightmare, because Americans could see that we're treating people like animals," he said Saturday.
Gillibrand, who was the first candidate to take the stage, signaled that the current administration's immigration policy is one of the catalyzing factors that pulled her into the nominating contest.
"It's one of the reasons why I'm running for president, because I cannot stand how [Trump] demonizes and demeans the most vulnerable in the world. And as president, I would not spend a dime on for-profit prisons to lock up children and families," she said to applause.
Inslee, who was last candidate to appear on stage, told reporters after he wrapped his remarks, "I just was morally shocked that a vice president would say we should be proud of locking children in cages."
"I'm shocked that a vice president would say that any American would think it's humane. ... I find that intolerable. We need humane treatment of people," he continued.
Franco Caliz, an attendee with the advocacy organization Community Change Action and a native of Nicaragua, told ABC News Friday that when it comes to differentiating between the field, "I'm really focused on policy."
"I think oftentimes it gets overlooked in the horserace," he said. "And I think Castro has been a real leader on immigration ... so I think its individual policies are really making a large difference to myself."
Among some of the attendees at this year's conference, who described immigration as a key issue for them amidst the turmoil at the U.S.-Mexico border, their focus appears to be on voting rights, which they suggest will broaden their strategy to counter Trump's hardline approach.
"My heart was grieving for those children in those cages," said Lisa Lima, an activist with the American Civil Liberties Union from Council Bluffs in the early caucus state of Iowa, who said her Mexican-born husband was detained. "If we're going to make change, it has to be at the ballot box. We need to make it accessible for everyone. ... Make that day sacred so people can get to the ballots, make it so people have the right to vote."
Another attendee, Barbara Helmick from Washington, D.C. echoed that sentiment in an interview with ABC News on Saturday, "There's a lot of things around the country that need to be fixed. Nobody should have to wait two hours in line to vote, that that should be easy, there should be no concerns about the validity of our votes."
"All of those voting issues intersect with everything else. It's important to me," she said.
ABC News' Jeffrey Cook contributed to this report.