Beto O’Rourke plans to present himself to the country as a changed candidate on Thursday, with his presidential campaign recast as a moral crusade against President Trump in the aftermath of a mass shooting in El Paso, his hometown.
Mr. O’Rourke, who represented the city in Congress until the start of this year, said he would abandon the relatively traditional approach he has so far taken — with limited success — and largely detach his travel from a primary calendar that tethers most candidates to a handful of early-voting states like Iowa and New Hampshire.
Instead, Mr. O’Rourke said he would now plan his political activities around confronting Mr. Trump in direct and personal terms, and highlighting what Mr. O’Rourke views as the injustices of Mr. Trump’s administration. He intends to seek out immigrant-rich towns to campaign in, and to make gun control a central issue.
Mr. O’Rourke was scheduled to outline his new approach to the campaign in a speech on Thursday morning. He planned to follow the speech with a trip on Friday to Mississippi, where federal authorities recently detained hundreds of undocumented immigrants in raids targeting workers in the poultry industry.
“I just have to be as clear and as strong as possible in calling this out and taking the fight to Donald Trump,” Mr. O’Rourke said in an interview on Wednesday evening. “In the immediate term, he is the greatest threat to this country, bar none.”
Mr. O’Rourke said he had begun to think of the campaign differently after being asked last week whether he would break away from his grieving city to attend the Iowa State Fair, a traditional stop on the presidential trail. He chose to skip the fair, and on Wednesday said he felt that kind of campaigning did not match the political moment.
“I don’t know that I’ve been doing a good enough job to match that threat with the urgency and the honesty and the clarity that it deserves,” Mr. O’Rourke said. “Being with those who have been denigrated and demeaned is more important than it has ever been.”
Beyond his imminent trip to Mississippi, Mr. O’Rourke said he envisioned campaign trips to visit Muslim communities that Mr. Trump had demonized, as well as people who were in jail and certain parts of the country that voted heavily for Mr. Trump.
“More than ever,” Mr. O’Rourke said, “we have to run a national campaign.”
It is difficult to foresee the political implications of Mr. O’Rourke’s decision on the crowded Democratic race. The field of candidates has not lacked for strong antagonists of Mr. Trump, nor for champions of liberal policies on immigration and gun control. By shifting his focus away from the early primary states, Mr. O’Rourke runs the risk of being overshadowed on multiple levels — on the national stage by better-known rivals, like Joseph R. Biden Jr. and Elizabeth Warren, and in Iowa and New Hampshire by more attentive underdogs, like Pete Buttigieg and Cory Booker.
Yet the approach Mr. O’Rourke envisions appears to be a direct extension of the agonized outcry to which he helped give voice after a white supremacist gunman murdered 22 people and injured dozens more in an El Paso Walmart. The killer told police he deliberately targeted Latinos, and in a manifesto echoed rhetoric about a migrant “invasion” that Mr. Trump and his political allies have regularly deployed.
Mr. O’Rourke responded to the attack in part by branding Mr. Trump a racist and white supremacist, and blaming him for having “created the conditions that made an attack like this possible and even likely.”
Mr. O’Rourke signaled in the interview that he would repeat that charge on Thursday, describing the country as facing a crisis brought on by “the hatred, the racism, the invitation to violence from this president.”
In some respects, Mr. O’Rourke’s new approach is an abrupt departure from his campaign style so far — one that has involved criticism of Mr. Trump but not a consuming focus on the president, with his campaign schedule defined by Mr. O’Rourke’s dogged personal courtship of voters in the early-voting states. His support in national polls has been hovering recently around 2 percent.
Mr. O’Rourke has also acknowledged, in both public and private settings, that the early stages of his presidential campaign gave the impression of excessive self-regard, starting with a romantic portrait on the cover of Vanity Fair that heralded his entry into the race.
In other ways, Mr. O’Rourke’s determination to proceed as a man unburdened by a traditional schedule of early-state rituals recalls the comparatively freewheeling and self-directed mode of campaigning he employed in his challenge to Senator Ted Cruz last year.
Over the last two weeks, Mr. O’Rourke has been a more resonant figure in the primary contest, speaking out from his wounded city in raw and emotional terms. And he has flashed glimpses of the traits that made him a hero to liberals in the midterm elections — his willingness to confront a right-wing adversary in plain language, for one, and his authentic passion on issues of immigration and national identity.
It remains to be seen whether Democrats are likely to find Mr. O’Rourke a similarly affecting spokesman on matters far outside El Paso and the immediate circumstances of the tragedy there. He has been facing a chorus of pleas, from Democrats in Texas and Washington, to leave the presidential race and run again for the Senate, challenging Senator John Cornyn, a senior Republican. Mr. O’Rourke has consistently rebuffed those entreaties.
An editorial in The Houston Chronicle this week urged him: “Beto, come home. Texas needs you.”
Mr. O’Rourke may still struggle to stand out in the presidential primary: He is far from the only Democratic candidate to blame Mr. Trump for creating a toxic and dangerous social atmosphere that has left Latinos and other minority groups vulnerable to violence. Nor is he the only candidate to design his campaign schedule around acts by Mr. Trump and other Republicans that Democrats find appalling.
Julián Castro, the former housing secretary and a fellow Texan, has been running ads on Fox News decrying the El Paso massacre that targeted people who “look like me.” In July, Mr. Booker, the New Jersey senator, crossed over the border with Mexico and returned with several migrants seeking asylum. And last week he delivered a searing speech on race at the Emanuel A.M.E. Church in Charleston, S.C., the site of another mass shooting by a white supremacist. In May, Senator Kirsten Gillibrand of New York campaigned in Atlanta after Georgia’s Republican-dominated government enacted strict new limits on abortion.
And around the Democrats’ first debate in Miami, a number of leading candidates — including Ms. Warren and her Senate colleagues, Kamala Harris and Bernie Sanders — visited a South Florida detention facility that was holding migrant children.
Asked if he saw himself as a distinctive voice in that crowd of candidates, Mr. O’Rourke said he did not think of his decision that way. But he felt he had a perspective to share, he said, grounded in his experiences in El Paso.
“I don’t always keep tabs on what all the other campaigns are doing,” he said. “I just know very clearly what it is that I have to do, and the urgency with which I feel it.”
Mr. O’Rourke added, “It has to change you, when this happens to your community.”