The new law gives US Customs and Border Protection more screening devices to detect fentanyl and other opioids that are being imported to the country. Trump said it feels like a "very giant step" in the opioid crisis but argued "it's not going to be a giant step, because no matter what you do, this is something that keeps pouring" into the country."
The President said he had the answer to the problem.
"There is an answer. I think I actually know the answer, but I'm not sure the country is ready for it yet," he said, before looking around at some of the lawmakers. "Does anybody know what I mean? I think so."
Some senators -- who attended the bill signing and are well versed on the opioid issue -- were puzzled by the comment when asked about them Thursday.
"I had no idea what answer that is," said Sen. Ron Johnson, a Wisconsin Republican. "I was intrigued, too, I'd like to know."
"Yeah, I wondered about that," said West Virginia Republican Sen. Shelley Moore Capito. "I didn't follow up and ask."
The West Virginia Republican continued: "When he said that, I thought, 'Uh, good for you if that's actually what he thinks?' But it's more complicated than one silver bullet."
Ohio Sen. Rob Portman said, "I remember something like that," before later adding: "I think the answer is, unfortunately, a lot of different things."
"I don't have any idea what the President was talking about," said Sen. Sherrod Brown, an Ohio Democrat. "I don't know if he even knew what he was talking about."
Asked if she had an idea as to what he was referring to, Sen. Jeanne Shaheen, D-New Hampshire, said, "Not at all."
The White House has not responded to a request to explain Trump's comment.
Given that the bill involved Customs and Border Protection, Capito said Trump was maybe talking about some sort of border security measure.
Brown didn't speculate on what the President meant, but he does hope part of Trump's solution involves more funding for treatment centers to help those with addiction.
Portman said he thought perhaps the President was talking about prevention measures. "I think it may have been the prevention side because that's ultimately the answer here to how you keep people from falling into this."