His words and the setting on the street that connects El Paso with Ciudad Juárez symbolized what his campaign said would be one of Mr. O’Rourke’s themes — a “unifying vision for bridging divides” to unite Americans from all walks of life.



But the speech by Mr. O’Rourke, a former three-term member of Congress, comes at a time of extraordinary discord over immigration, with a surge of migrants trying to enter the United States and President Trump threatening to seal off the border next week.

El Paso has been a flash point for much of that unrest, with hundreds of migrants now being held in a makeshift encampment under a bridge near where Mr. O’Rourke was speaking.

The encampment, where immigration officials are detaining people behind razor wire with little hot food, was set up last week when El Paso’s main border processing center reached overflow capacity following the largest influx of migrants in years.

Acknowledging the plight of the migrants, Mr. O’Rourke said, “Let us remember that every single one of us, including those who are just three or four blocks from here detained under the international bridge — behind chain-link fence and barbed wire — they are our fellow human beings and deserve to be treated like our fellow human beings.”

Mr. O’Rourke, who also held rallies Saturday in Houston and outside the state’s capitol in Austin, stressed not only immigration but also health care, education, climate change, criminal justice reform, the economy, voting rights and racial inequality. All are topics that have emerged as major issues in the effort by Democrats to unseat Mr. Trump in 2020.