As the divisive primary season is about to wind up, however, Sanders, a self-described democratic socialist, and the roughly one million voters who "feel the Bern" will soon face a tough choice of whether or not to line up behind the very person they has been ripping for months.

So far, Sanders has offered mixed and sometimes nuanced response as to what would be his next step after the crucial Democratic California primary on June 7, when 475 pledged delegates will be up for grabs.

Senator Sanders facing tough choice after California primary

Speaking in an interview with NBC News on Sunday, Sanders touted his better performance than Clinton in hypothetical matchups against presumptive Republican nominee Donald Trump to justify his continued stay in the race despite Clinton's near-insurmountable delegate lead.

"Right now, in every major poll, national poll and statewide poll done in the last month, six weeks, we are defeating Trump, often by big numbers and always at a larger margin than Secretary Clinton is," said Sanders.

According to PolitiFact.com, a project dedicated to "fact-check" of statements of politicians and the federal government, Sanders was correct that he fared better against Trump than Clinton did in all polls over the last six weeks.

Sanders' remarks came at a time when Clinton and party elites were scrambling to salvage the party unity from the damage inflicted by the insurgency of Sanders' campaign.

According to the most recent YouGov poll, 61 percent of Sanders supporters have an unfavorable opinion of Clinton in May.

However, in his remarks last weekend, Sanders surprisingly relented in his slash of the Democratic primary, walking back on his previous criticism of the process as "rigged" in favor of Clinton.

"I think we have an uphill fight, but there is just a possibility that we may end up at the end of this nominating process with more pledged delegates than Hillary Clinton," said Sanders on Saturday in an interview with CBS News.

"What has upset me, and what I think is -- I wouldn't use the word 'rigged' because we knew what the rules were -- but what is really dumb, is that you have closed primaries, like in New York State, where three million people who were Democrats or Republicans could not participate," he said.

Also, when Sanders were asked whether or not he would be Clinton's running mate in the latest interview with NBC News on Sunday, Sanders did not rule out the possibility.

"Here we are in California, I'm knocking my brains out to win the Democratic nomination," said Sanders in the interview. "What happens afterwards, we will see," said Sanders.