Democrats escalated their attacks on President Donald Trump's policy of separating immigrant children from parents who illegally cross the Mexican border, as public outrage over the practice balloons into an election-year controversy for Republicans.

Several Democratic lawmakers, including Sens. Jeff Merkley of Oregon and Chris Van Hollen of Maryland, are traveling to the Rio Grande Valley area in Texas on Sunday to meet with U.S. border authorities and tour a former Walmart Inc. store that's been converted into a detention center for nearly 1,500 immigrant boys. Texas Congressman Beto O'Rourke, who's challenging Republican Sen. Ted Cruz in November, planned to visit a a new facility opened near El Paso he described as a "tent city."

"I'd like to say it's un-American, but it's happening right now in America. And it's on all of us — not just the Trump administration — it's on all of us," O'Rourke said Sunday on CNN's "State of the Union." "I hope to produce the outrage and the public pressure to force those in power to do the right thing."