The fact-finding tours, detailed in interviews with more than two dozen lawmakers and aides, are sometimes sanitized for the V.I.P.s who take them, as the Trump administration works to put the best face on an often inhumane situation. But they have yielded moments of raw emotion and glimpses of human suffering that have prompted passionate testimony, viral videos of lawmakers on their tours, new legislative proposals and, in one case, a book.

Every lawmaker who makes the trek south agrees on the system’s dysfunction, but few emerge with changed minds or drastically different perspectives. The bigger question of how to avoid having the immigration crisis once again languish remains unanswered.

The Democrat-led House this week approved two bills largely on party lines that would hold the Department of Homeland Security to higher accountability and medical standards for immigrant holding facilities, but its chances in the Republican-held Senate are slim to none. And in a committee hearing over funding the border, senators clashed over how much money to give to the president’s wall at the southwestern border, even after the chamber’s majority voted to end his national emergency declaration there.

“The goal was, everybody could see it and say, ‘O.K., we’ve all seen it. We can come to a common set of conclusions on how to be able to resolve it,’” Senator James Lankford, Republican of Oklahoma, said of his recent visit to the border. “But I’m not hearing that.”

“Maybe, lessons learned.”

What lawmakers take away from the border usually depends on what they are looking for.

Representative Andy Biggs, Republican of Arizona, organized multiple summer trips focusing on the enforcement side, giving lawmakers the chance to tour fragments of Mr. Trump’s border wall and to speak with local law enforcement, as well as with property owners whose land runs close to the border.

Democrats tend to focus instead on the humanitarian side. Representative Veronica Escobar of Texas has led several groups to her El Paso district, organizing interviews with migrants detained in Juárez, Mexico, and taking her colleagues to the road between the two countries.