"Believe me. I will beat Hillary," he said in an interview that aired on "The Lead with Jake Tapper."
Trump questioned whether Clinton would even be able to continue her campaign due to her use of her personal email at the State Department.
"What she did is a criminal act. She burned up the emails. She got rid of her hard drive," he said.
Trump also suggested that Democratic candidate Bernie Sanders, the senator from Vermont, could end up with more competition.
"I think that other people are going to probably join the race, eventually, like maybe (Vice President Joe) Biden and other people," he said.
As for the Republican Party, Trump said he has recently had "very nice" conversations with Reince Priebus, the head of the Republican National Committee.
"I respect him," Trump said.
Trump's interactions with Priebus have come under close scrutiny after the businessman said he was more likely to run as a third-party candidate if he felt the party establishment wasn't treating him fairly. The relationship hit a particular rough patch when the committee scolded Trump earlier this month for making disparaging comments about Sen. John McCain's service in the Vietnam War.
But Trump repeated Wednesday that the best path forward for him is to win the GOP nomination.