But he went ahead Wednesday with a scheduled trip to Duluth, Minnesota, including a nighttime "Make America Great Again" campaign rally for a Republican congressional candidate.
Trump did not say when the picnic on the South Lawn, which is attended by lawmakers and their families, as well as White House and senior administration officials, would be rescheduled. He announced the postponement as he sat down at the White House with Republican members of the House and Senate.
"I was just walking over to the Oval Office and I said, 'You know, it doesn't feel right to have a picnic for Congress when we're working on - doing something very important,'" Trump said. "We have many things that are important. We're talking about trade. We're talking about many, many things, but it didn't feel exactly right to me."
Trump, who opened the meeting by commenting on the border situation, has been under mounting pressure to reverse the administration's "zero-tolerance" immigration enforcement policy. Under the policy, people who enter the country illegally at the U.S.-Mexico border are criminally prosecuted while any children are sent to detention centers.
More than 2,300 migrant children have been separated from their families at the border since May, the government said.
Before departing for Minnesota, Trump signed an executive order to keep families together at the border.
"So we will be officially postponing the congressional picnic for tomorrow. We'll make it another time when things are going extremely well. And they are going for the country extremely well," the president said. "We have record-setting numbers in every way economically, but we want to solve this immigration problem, which is going on for four years more. It's been going on forever, and we want to see if we can solve it, so we are canceling, we're postponing the congressional picnic tomorrow."
Trump did not say what would happen to the steaks and other meats cooks had been pre-grilling at the White House in preparation for the picnic.
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