"Bernie Sanders has been treated terribly by the Democrats -- both with delegates & otherwise. He should show them, and run as an independent," Trump tweeted Tuesday.
Sanders' wife, Jane Sanders, quickly dismissed the idea in an interview with CNN's Wolf Blitzer Tuesday afternoon.
"We've been very clear right from the beginning that we will not play the role of spoiler," she said. "The reason that he was active and he decided to run in the Democratic Party was just that: We cannot afford a Republican in the White House. We cannot afford a Republican appointing Supreme Court justices. So Bernie will not be running as an independent."
Trump, who has criticized the Republican nominating process as "rigged," has occasionally cited Sanders' deficit in the Democratic delegate fight as an example of how both parties' systems are corrupt.
Of course, a Sanders independent bid would likely benefit Trump in a general election campaign, pulling support away from Hillary Clinton on the left, were she the Democratic candidate.
Sanders, meanwhile, has said he would remain in the race at least until June 7, the final primary voting day.
"I think we've got a path to victory and we're going to fight this until the last vote is cast," he told CNN's Chris Cuomo Tuesday on "New Day." "So we're in this until the end."
"I think we have a shot in Pennsylvania, Connecticut, Rhode Island. Maybe Delaware. I think Maryland's going to be tougher for us," he said.
An independent bid by Trump himself has been much speculated about in the course of the 2016 race, with the businessman fluctuating on his claims of loyalty to the GOP. He's signed a party loyalty pledge, but declined to rule out the possibility
when pressed during an interview earlier this month on "Fox News Sunday."
Later Tuesday, Trump was featured in a Sanders fundraising email, which included a photo of the Clintons at Trump's wedding in 2005.
"Here's the truth: no matter what the Clinton campaign says, there is one candidate in this race Donald Trump said would make a great president, and another that he would never want to face in November," the email read. "And that's because poll after poll after poll shows that he wouldn't stand a chance against our political revolution."