At a Las Vegas rally, Trump, the presumptive Republican nominee, implied that Sanders is waiting for Clinton to be indicted so he can then claim the Democratic nomination himself at the party's convention in Philadelphia.
"Crazy Bernie," Trump said of the Vermont senator. "He's crazy as a bed bug, but he doesn't quit."
"He's waiting for the FBI to do what everybody thinks they're going to do," Trump added. "I think he's saying, 'Let's hang in there because its ultimately called the FBI... We'll see if the right thing happens. Everybody knows what the right thing is."
Trump made a similar rally at his second rally on Saturday, in Phoenix.
"Bernie, he doesn't quit," Trump said. "He's in there bitching."
Clinton has called the private email server a mistake, but has insisted everything was legal and that she would be cleared.
Sanders came up well short behind Clinton in the Democratic delegate fight. Though the primaries are over Sanders has not dropped out and endorsed Clinton.
On Saturday Trump also pushed back on reports that Republican activists were plotting to deny him the GOP nomination at the Cleveland convention this summer. Trump noted he beat back 16 primary rivals and won a record number of votes.
"Who are they going to pick? I beat everybody. I beat the hell out of them," Trump told the Las Vegas crowd. "And we're going to beat Hillary. And it would be helpful if the Republicans could help us a bit," Trump added.
But some Republican delegates are still supporting anybody but the presumptive Republican nominee. Some are pushing for a "conscience clause" that would allow delegates to vote against the presumptive nominee.
Kendal Unruh, a Colorado delegate, organized a call with dozens of other delegates Thursday night to discuss ways to block Trump at the convention. The group, Unruh said, marks the coalescing of disparate "pockets of resistance" -- including backers of Sen. Ted Cruz, Sen. Marco Rubio and Ohio Gov. John Kasich -- which had been opposing Trump with little success.
The Republican National Committee, which is supporting the Trump campaign, dismissed the effort Friday.
"The extent of this effort is a bunch of random people tweeting about it, full stop," said RNC chief strategist Sean Spicer.
However, Trump did allude to some dissention in Republican ranks. He argued that if GOP establishment types didn't fully support his campaign he could self-fund, rather than relying on the party apparatus to help bring in donations. Throughout much of the primary process Trump pledged to pay for the campaign himself, only to begin accepting donations later on.
"Life is like two-way street, right?" Trump said. "Otherwise I'll just keep doing what I'm doing. I'll just keep funding my own campaign. I'm ok with that. That's the easy way. I mean for me, that's the easy way. But, hopefully I can continue to go the way we're going, and this weekend we raised a lot of money. We've raised a lot of money for the Republican Party. We'll keep doing it, because we do have tremendous support within the party that I can tell you."
At a second rally Saturday, in Phoenix, Trump said reluctant Republicans would eventually come around to his White House bid.
"We have some Republicans that aren't there," Trump said. "The Republicans should stick together. I don't think it's going to matter that much in terms of whether I win."