Sen. Jeff Merkley Jeffrey (Jeff) Alan MerkleyThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Sunday shows - Trump team defends coronavirus response Oregon senator says Trump's blame on 'forest management' for wildfires is 'just a big and devastating lie' MORE (D-Ore.) led a group of Democratic lawmakers to the southern border in Texas on Sunday amid growing backlash against the Trump administration's policy of separating families who have crossed the border illegally.

Merkley was joined in McAllen, Texas, by Sen. Chris Van Hollen Christopher (Chris) Van HollenCongress must finish work on popular conservation bill before time runs out Democrats fear Russia interference could spoil bid to retake Senate Mid-Atlantic states sue EPA over Chesapeake Bay pollution MORE (D-Md.), as well as Texas Reps. Filemon Vela Filemon Bartolome VelaHispanic Caucus asks for Department of Labor meeting on COVID in meatpacking plants The Hill's Campaign Report: Biden builds big lead in battleground Florida Texas Democrat proposes COVID-19 victims' compensation fund MORE (D), Vicente González (D), and Sheila Jackson Lee Sheila Jackson LeeGrand jury charges no officers in Breonna Taylor death Hillicon Valley: Murky TikTok deal raises questions about China's role | Twitter investigating automated image previews over apparent algorithmic bias | House approves bill making hacking federal voting systems a crime House approves legislation making hacking voting systems a federal crime MORE (D).

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Democratic Reps. David Cicilline David Nicola CicillineClark rolls out endorsements in assistant Speaker race Races heat up for House leadership posts The folly of Cicilline's 'Glass-Steagall for Tech' MORE (R.I.), Peter Welch Peter Francis WelchShakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' Vermont Rep. Peter Welch easily wins primary Vermont has a chance to show how bipartisanship can tackle systemic racism MORE (Vt.), and Mark Pocan Mark William PocanOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Democrats call for investigation into Pentagon redirecting COVID-19 funds Clark rolls out endorsements in assistant Speaker race MORE (Wis.) also traveled to the border on Sunday.

The group of lawmakers toured the Customs and Border Protection processing centers and looked to find out more information about how the agency processed immigrants illegally entering the U.S., including the Trump administration policy that prosecutes parents crossing the border illegally, thus separating them from their children.

The visit on Sunday was billed by organizers as "#FathersDayofAction."

WATCH: I’m on the border investigating @realDonaldTrump’s cruel policy of ripping children away from their parents. #FathersDayofAction pic.twitter.com/cLVMQmmIh1 — Senator Jeff Merkley (@SenJeffMerkley) June 17, 2018

"Here's what's going on. It's a comprehensive strategy of preventing people from seeking asylum. So at the bridges, those who already have documents, passports and so forth are let in while those seeking asylum are kept in the no man's land between Mexico and the United States," Merkley told CNN.

"And so they're going to cross the border and that's where the administration is saying 'oh, they broke the law crossing the border outside the border checkpoint. Now we'll arrest them and treat them as criminals and take their kids away. I have also heard though, of a number of stories of people who did cross at the official checkpoints who have also been charged with a crime and separated from their children," he continued.

"This is a deliberate and inhumane policy, and we're here to say to President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE, end it and end it today," Van Hollen said in the same interview.

Merkley made headlines earlier this month when he shared a video of him attempting to enter an immigration detention facility in Texas. He was ultimately turned away by officials.

The lawmakers' visit on Sunday comes as the administration scrambles to defend the policy in the face of growing backlash.

Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE invoked the Bible to defend the policy on Thursday, urging law and order at the border, while President Trump blamed Democrats for the policy on Friday.

"The Democrats are forcing the breakup of families at the Border with their horrible and cruel legislative agenda. Any Immigration Bill MUST HAVE full funding for the Wall, end Catch & Release, Visa Lottery and Chain, and go to Merit Based Immigration. Go for it! WIN!" the president tweeted.

The Democrats are forcing the breakup of families at the Border with their horrible and cruel legislative agenda. Any Immigration Bill MUST HAVE full funding for the Wall, end Catch & Release, Visa Lottery and Chain, and go to Merit Based Immigration. Go for it! WIN! — Donald J. Trump (@realDonaldTrump) June 15, 2018

Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenMore than million in DHS contracts awarded to firm of acting secretary's wife: report DHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections MORE issued a series of tweets on Sunday, denying that the administration had a policy of separating families at the border.

"This misreporting by Members, press & advocacy groups must stop. It is irresponsible and unproductive. As I have said many times before, if you are seeking asylum for your family, there is no reason to break the law and illegally cross between ports of entry," Nielsen said.

"You are not breaking the law by seeking asylum at a port of entry," she continued. "For those seeking asylum at ports of entry, we have continued the policy from previous Administrations and will only separate if the child is in danger, there is no custodial relationship between 'family' members, or if the adult has broken a law."