Bernie Sanders on Thursday laughed off Donald Trump's attempts to goad him into launching an independent bid for president, but notably did not rule out the prospect.
"I think there is a little bit of self-service there from Donald Trump," the Vermont senator said in an appearance on "Jimmy Kimmel Live."
Kimmel had given Trump, who appeared on his show Wednesday, an opportunity to pass on a question for Sanders.
"Bernie, you have been treated very unfairly," the Republicans' presidential nominee asked, according to Kimmel. "Both primary systems are rigged, but in particular the Democrats' ridiculous system of superdelegates. Will you run as an independent when [Democratic National Committee Chairwoman] Debbie Wasserman Schultz and the party bosses steal this nomination away from you?"
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"You think he's really worried about me?" Sanders joked. "I really appreciate his concern for me. I know it comes straight from his heart."
But he didn't directly answer the question.
"What I hope will happen is in fact that I will run against him as the Democratic nominee for president of the United States," he said, "and if I do, we're going to beat him and beat him bad."
The host had given Sanders the same option ahead of Trump's appearance; Sanders asked if Trump was willing to debate, and the former reality television star said he would – for charity.
Trump, who has nicknamed him "Crazy Bernie," has for several weeks feigned concern for Sanders, playing off Sanders' supporters accusations that the Democratic National Committee had tilted the scales in favor of Hillary Clinton, the party's front-runner.
Bernie Sanders has been treated terribly by the Democrats—both with delegates & otherwise. He should show them, and run as an Independent!
— Donald J. Trump (@realDonaldTrump) April 26, 2016
With just a handful of states yet to hold their primaries, Sanders trails Clinton by nearly 300 pledged delegates and more than 3 million votes. To overtake her, Sanders would have to win 68 percent of the delegates still available – far exceeding the 46 percent he has so far – and convince a majority of superdelegates to swing his way.
If Sanders were indeed considering a third-party run, however, it would contradict his vow not to do so if he lost the Democratic nomination.
"If it happens that I do not win that process, would I run outside of the system? No," he told the Hispanic Chamber of Congress in July. "I made the promise that I would not and I'll keep that promise."
Jane Sanders, his wife and a top campaign surrogate, reiterated the pledge after Trump made sympathy for Sanders' treatment a regular part of his stump speech.
"We've been very clear right from the beginning that we will not play the role of spoiler," his wife, Jane Sanders, told CNN in late April. "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."
Still, Democrats have publicly worried that Sanders, having fallen out of real contention in the primary but refusing to drop out, would damage Clinton's ability to unite the party against Trump in the fall.
At campaign rallies, the senator has vacillated, sometimes toning down his rhetoric against Clinton and aiming his fire at Trump, but other times blasting Clinton, Wasserman Schultz and the system he says has hamstrung his campaign.
While Sanders has promised to fight for every vote through the end of the primaries – and is doing everything he can to keep his supporters engaged – he has privately assured Democrats he will work for unity.
Last week, Sanders called several Senate colleagues, insisting he would go to bat for Clinton if she were the nominee.
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