El Paso, Texas (CNN) Beto O'Rourke returned to the campaign trail Thursday with a new clarity and a dire warning: Donald Trump has broken America's political institutions and poses a threat so grave that -- unless the President is confronted -- "we as a country will die in our sleep."

Twelve days after pausing his campaign to return home in the wake of the mass shooting that left 22 dead at an El Paso Walmart, the former Texas congressman announced his return to the 2020 race with a speech delivered in a park overlooking his hometown and neighboring Ciudad Juárez, Mexico.

He said he is eschewing the pageantry of the road to the White House -- such as stops at the Iowa State Fair -- to refocus his bid for the Democratic nomination around the people and communities most threatened by Trump's policies and rhetoric.

In his speech, O'Rourke said Trump's racist attacks on black and brown people, particularly immigrants, changed "who we are as a country."

"Our institutions have failed" in shielding the nation from the forces Trump's words have unleashed, he said.

"They have been impotent in the face of the greatest threat that we have ever known -- one that we experienced first-hand here in El Paso a week ago Saturday," he said. "It's almost as if the bigger the lie, the more obvious the injustice, the more furious the pace of this bizarre behavior, the more incapable we are of seeing it and clearly naming it and acting against it."

"If we do not wake up to this threat, then we as a country will die in our sleep," O'Rourke said. "The response to this has to be that each of us make a commitment to see clearly, to speak honestly, and to act decisively in this moment of truth."

He faulted a "Congress too craven to act" and "a democracy not up to the task" because it is controlled by wealthy interests. He also lambasted "the complicity and the silence of those who are in positions of public trust."

After months of lagging in the polls, Thursday's speech with the national media tuned in was O'Rourke's best chance -- and perhaps his last one -- to show the mold-breaking promise that had once evoked comparisons to Robert F. Kennedy and Barack Obama.

He said that "there's a big part of me that wants to stay here and be with my family and be with my community. I love El Paso."

"There have even been some that suggested that I stay in Texas and run for Senate," he said. "But that would not be good enough for this community. That would not be good enough for El Paso. That would not be good enough for this country. We must take the fight directly to the source of this problem -- that person who has caused this pain and placed this country in this moment of peril. And that is Donald Trump."

O'Rourke repeatedly used a refrain — "I see more clearly now than I ever have before" — in describing the danger of Trump's attacks on immigrants, America's proliferation of guns and more. The line underscored how O'Rourke is attempting to sharpen his message and jump-start his campaign.

Even as he pledged to remain a presidential candidate, O'Rourke said he couldn't tolerate the frivolity of some of the rituals of the road to the White House -- such as gobbling corn dogs at the Iowa State Fair, which he skipped last weekend -- noting he "cannot go back to that."

Instead, O'Rourke said he'll focus on visiting communities and populations that Trump has attacked. That starts later Thursday when he travels to Mississippi, where more than 600 undocumented workers at food processing plants were arrested by immigration authorities in a massive raid last week

"To those places where Donald Trump has been terrorizing and terrifying and demeaning our fellow Americans, that's where you will find me in this campaign," O'Rourke said.

When asked by a reporter why Democrats in the early-voting states in the race for the Democratic nomination -- Iowa, New Hampshire, Nevada and South Carolina -- would vote for him, O'Rourke replied that "everyone's story" should be "brought in."

"This is one of the most diverse countries on the face of the planet. We have to make sure that everyone's story is brought in, and if we restrict ourselves to only being in the early nominating states, we will have failed in that incredibly important task," he said.

O'Rourke, who has long backed universal background checks, red flag laws and a ban on assault weapons sales, also on Thursday unveiled a new -- and farther-reaching -- proposal to eliminate those assault weapons: a mandatory buy-back

He said he met a woman at a hospital who was a victim of the Walmart shooting, and whose husband was shot and has not yet awoken, who told him she owns an AK-47 -- but would gladly give it away if that's what it took to make the country safer.

"I know that this is not politically easy," he told CNN when asked about the proposal. "It's frankly why far too few people have proposed it; it's frankly why I have not proposed it in the past. I've said, 'This is something we should consider, I want to think about it, I want to talk to people about it.' I've thought about it. I've talked to people. I've listened to that survivor. And now, beyond a shadow of a doubt, regardless of what it does to our prospects going forward, you've got to speak the truth and be clear about where the solutions are."

O'Rourke views much of American politics through the prism of his hometown, which is a bilingual and binational community on the US-Mexico border that leaders here, including O'Rourke and Democratic Rep. Veronica Escobar, sometimes bill as "the new Ellis Island" for immigrants and asylum-seekers. His speech Thursday portrayed the area as under attack by Trump -- and O'Rourke as obligated to do what he could to fight back.

"I want to be the kind of leader for this country," he said, "that El Paso has raised me and taught me to be."