His progressive brand of politics appeal to a wide array of Americans, especially young people.
But some of his recent words and actions have rubbed many on the left, especially those who are pro-choice, the wrong way.
Sanders recently endorsed Heath Mello, a Democratic candidate for mayor in Omaha, who as a state senator reportedly supported a ban on abortions at 20 weeks and mandatory ultrasounds for women seeking abortions.
Because of Mello's record on reproductive rights, Sanders's support for him has a lot of people up in arms.
If you're unfamiliar with what a ban on abortions after 20 weeks entails, almost all abortions (roughly 99 percent), occur before 21 weeks.
Moreover, supporting mandatory ultrasounds for abortions is seen by many as a clear attempt to induce guilt during a process that can already be extremely difficult.
This is why pro-choice groups like NARAL have been very critical of Sanders and the Democratic National Committee for supporting Mello.
In a statement, NARAL Pro-Choice President Ilyse Hogue said,
The actions... by the DNC to embrace and support a candidate for office who will strip women -- one of the most critical constituencies for the party -- of our basic rights and freedom is not only disappointing, it is politically stupid.
Tom Perez, chairman of the Democratic National Committee (DNC), initially supported Mello, but seems to have walked back on this.
In a statement on Friday, Perez said he "fundamentally disagree[s] with Heath Mello's personal beliefs about women's reproductive health."
Perez said, "every Democrat," and all Americans for that matter, "should support a woman's right to make her own choices about her body and her health."
The DNC chairman said this "is not negotiable" and "should not change city by city or state by state."
Sanders, who recently traveled to Omaha to attend a rally for Mello, defended his decision to support Mello by arguing you can't cut people out of the party just because you don't agree with them on 100 percent of the issues.
He said that this is especially true "in some conservative states."
Speaking with NPR, Sanders said,
We have got to appreciate where people come from, and do our best to fight for the pro-choice agenda. But I think you just can't exclude people who disagree with us on one issue.
He contended reproductive rights are in better hands if Democrats control state and local governments around the country.
But it's clear many feel reproductive rights are a non-negotiable issue and believe Democrats must be aggressively pro-choice.
In spite of the fact Mello recently promised he would “never do anything to restrict access to reproductive health care," he's still facing criticism.
Still, many of Sanders' supporters and others have rushed to his defense and feel the situation has been exaggerated and misrepresented.
The debate over this, among other issues, has reignited the conversation over the divisiveness that's plagued Democrats since the US presidential campaign.
It seems the Democratic party is still struggling to come together and find its way in the era of Trump.