“I mean, how can you lose like this?" Trump said. "He really isn’t even a Democrat. But he said he’s a socialist, and I think he may be a step beyond a socialist."
Clinton’s campaign has increasingly acknowledged the tough battle it believes the former secretary of state faces against Sanders in early-voting states.
Clinton has recently begun to join his wife on the campaign trail.
"She came out with a little bit of a statement about me,” Trump said of Hillary Clinton, "and I came out with a very big statement about her and Bill, and she stopped talking about me all of the sudden.”
Trump that he hadn't "even started" going after Clinton yet, saying his recent jab at her husband's infidelity had succeeded in quieting the couple.
"I'm winning against Hillary one-on-one," Trump said, touting his latest poll numbers. "And I haven't even started on her yet, although last week I did a little bit. But we haven't even started."
Fallon also noted that Trump had said he believed President Barack Obama had cried during remarks this month about gun violence – despite some conservative pundits’ claims he had faked it.
“Do you cry ever?” Fallon asked the billionaire, who projects a tough image on the trail.
“Yeah,” Trump responded, "When I was one, I cried.”
The real estate mogul also said his and Clinton's candidacies may have a positive effect on voting in the United States if they high turnout at the ballot box.
"That's a good thing, because people don't vote that much in this country," Trump said. "So that would be an amazing thing if that happened."