Trump tried to put the blame on Democrats as he left Washington, saying they didn't want to provide the bed space needed to detain unsafe people wanting to come into the U.S.
"We were, I think, the No. 2 or No. 3 safest city before the fence went up and we progressed into No. 1", he told Fox News.
President Donald Trump, who is insisting on funding for a southern border wall, sent out a tweet claiming that "The Democrats do not want us to detain, or send back, criminal aliens!" But that's not true.
O'Rourke, who lost in his bid for a U.S. Senate seat in Texas, promised to blast Trump for stoking "false fear" about immigrants and telling "lies" about his hometown El Paso, which Trump said was a risky place before it had a border fence.
The El Paso Times reported that this was not the case.
El Paso is a Texas border city adjacent to Mexico's Ciudad Juarez.
New fencing was erected starting in 2008 and it was completed in 2009.
The Trump campaign released a video showing El Paso residents saying the wall helped reduce crime.
Earlier in the day Monday, O'Rourke plans to join Democratic Rep. Veronica Escobar - a longtime ally who took his former seat in Congress after his failed bid to unseat Republican Sen. Ted Cruz of Texas. While few Democratic candidates have focused on immigration in their launches, O'Rourke has described Trump's calls for the wall as the "cynical rhetoric of war, of invasions, of fear". El Paso's had an estimated population of 683,577 people in 2017, according to the U.S. Census Bureau. So far, O'Rourke has not made a decision.
Violent crime did not drop in El Paso "immediately" after a "powerful barrier" was put up.
"I understand our competitor has a line, too, but it's a tiny little line", Trump said.
President Trump is gearing up for his first rally of the 2020 campaign season. Weakened by the longest government shutdown in American history, Trump is also contending with the ongoing investigation into Russian election meddling and a flurry of investigations by newly empowered majority Democrats in the House.