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Senator Jeff Merkley has witnessed some atrocious scenes at migrant detention centers along the Texas-Mexico border. He described one where “hundreds” of children were ripped out of their parents’ arms and sorted into chain-link cages, standing in single-file lines from shortest to tallest.

“The shortest one was in front and he was just knee-high to a grasshopper, maybe four years old,” Merkley told Mother Jones’ editor-in-chief Clara Jeffery in August at the Commonwealth Club in San Francisco. “I was stunned.”

Despite Donald Trump’s claims that he’s “the least racist person,” Merkley said the president’s anti-immigration rhetoric is rooted in racism. When Jeffery asked him if he thought President Trump was a racist, Merkley responded without hesitation, “Yes, I do.”

Listen to Clara Jeffery interview Jeff Merkley on the latest episode of the Mother Jones Podcast below:

“We have a president who campaigned on division,” said Merkley. “When he came into office he continued to pour fuel on the divisions, but he came to find the easiest target is immigrants. Immigrants not from Europe: immigrants from south of the border.”

Merkley made headlines last year when he live-streamed his attempt to look inside a former Wal-Mart that’s now home to 1,500 migrant children in Brownsville, Texas. The video went viral and ignited a national outrage about the treatment of people who were forced to live there. Soon after, he received permission to tour the facility and became the first member of Congress to tour that particular location.

Since then, Merkley has spearheaded legislative efforts to shut down detention centers for migrant children. His new book, America Is Better Than This: Trump’s War Against Migrant Families, tells the story of how he, a junior senator from Oregon with no experience on immigration issues in Congress, became a leading advocate for immigration reform against President Trump’s anti-immigration campaign.

It’s clear that immigration will be a key issue in the 2020 presidential election. To beat President Trump, Merkley said, voters have a moral duty to speak up and fight back.

“Lady Liberty’s torch has been snuffed out by this administration and we need to recognize that this is a pretty dark, heavy time for our country but we have an opportunity to change that; an opportunity in our daily conversations, an opportunity with our resources,” said Merkley, who will not be running for president, but, instead, will pursue re-election in the Senate. “But let’s also use our weight and time and energy to put America back on track in November 2020.”