Addressing the nation from the Oval Office for the first time, Trump argued for funding on security and humanitarian grounds as he sought to put pressure on newly empowered Democrats amid an extended partial government shutdown.
Trump called on Democrats to return to the White House to meet with him, saying it was "immoral" for "politicians to do nothing." Previous meetings have led to no agreement.
Responding in their own televised remarks, Democratic House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer accused Trump of misrepresenting the situation on the border as they urged him to reopen closed government departments and turn loose paychecks for hundreds of thousands of workers.
Schumer said Trump "just used the backdrop of the Oval Office to manufacture a crisis, stoke fear and divert attention from the turmoil in his administration."
Trump, who has long railed against illegal immigration at the border, has recently seized on humanitarian concerns to argue there is a broader crisis that can only be solved with a wall. But critics say the security risks are overblown and the administration is at least partly to blame for the humanitarian situation.
Trump used emotional language, referring to Americans who were killed by people in the country illegally, saying: "I've met with dozens of families whose loved ones were stolen by illegal immigration. I've held the hands of the weeping mothers and embraced the grief-stricken fathers. So sad. So terrible."
The president often highlights such incidents, though studies over several years have found immigrants are less likely to commit crimes than people born in the United States.
Trump has been discussing the idea of declaring a national emergency to allow him to move forward with the wall without getting congressional approval for the $5.7 billion he's requested. But he did not mention that Tuesday night.
With his use of a formal White House speech instead of his favored Twitter blasts, Trump embraced the ceremonial trappings of his office as he tries to exit a political quagmire of his own making. For weeks he has dug in on a signature campaign promise to his base voters, the pledge to build an impregnable "beautiful" wall along the U.S.-Mexico border.
The partial government shutdown reached its 18th day, making the closure the second-longest in history. Hundreds of thousands of federal workers are going without pay, and government disruptions are hitting home with everyday Americans.