On Wednesday night in Las Vegas, they made their cases with the other candidate mere feet away.
"I am proud to be running in a Democratic primary with my opponents. They have a lot of good ideas and we share a lot of the same values," Clinton said with Sanders sitting at a dinner table nearby. "But your choice in the caucus really matters. On February 20th you will begin the process of choosing a president who has what it takes to stand up to the Republicans, to make a real difference for American families."
She then added, digging her critique a little deeper, "A president who can get the job done and not just on a few issue, but on all the complex challenges we face."
The comment was not taken kindly by Sanders supporters, many of whom booed the former secretary of state at points during her speech.
Sanders, speaking after Clinton at the dinner, responded in kind, teeing up his comment on electability by saying he wanted to be "clear" and "a little bit political" in his comments.
"All of us want to make sure that we defeat right wing extremism, that we make certain that no Republicans become president of the United States, all of us are united that we are going to take back the Senate and that we are going to do well all over this country," Sanders said. "But let me be very clear: That result will not happen with establishment politics and establishment economics. The only way that Democrats win elections, is when we have a large voter turnout."
Sanders supporters - keyed into the back and forth on electability - jumped to their feet at this comment. Clinton supporters did not, in part because many of them left after their candidate had finished speaking.
Clinton and Sanders were the main events at the dinner, but all three Democratic candidates - including former Maryland Gov. Martin O'Malley - tried to court their party's faithful at the Nevada Democrats "Battle Born/Battleground" First in the West Caucus Dinner.
But O'Malley, despite a more polished speech than past Democratic events, was largely an afterthought. While Clinton and Sanders supporters sat on opposing sides of the room, challenging each other to who could chant louder, O'Malley didn't have a noticeable cheering section.
Divided into camps
The audience was largely made up of decided voters. Campaigns gave supporters tickets to to the event and supplied them with different cheering paraphernalia. Clinton's supporters waved their now-common blue glow sticks, while Sanders' backers blew air-horns and hummed into vuvuzelas, the horns that became known for their annoying buzz during the 2010 World Cup.
"That music is really beautiful," Sanders said sarcastically to his supporters, before motioning for them to tone it down.
The argument over whether Clinton or Sanders is most electable has been playing out for the last three days on the Democratic side of the presidential campaign.
Touring through New Hampshire and Iowa, Clinton stressed her experience and her ability to hit the ground running if she were to win in November. She also urged her supporters to think about what a Republican presidency would be like, and cast her self as the best Democrat to stop that possibility.
"Let me ask you all to think hard about this job that you are interviewing for," Clinton said Tuesday night in Council Bluffs. "Think hard about the people who are presenting themselves to you, their experience, their qualifications, their positions, but particularly for those of us who are Democrats, their electability."
This comments annoyed Sanders aides - and the candidate.
Michael Briggs, Sanders' spokesman, quickly issued a statement in response to Clinton that questioned her ability to generate enough excitement to beat someone like Republican frontrunner Donald Trump.
And when asked by CNN on Wednesday - before his dinner speech - whether he is more electable than Clinton, the senator bluntly said, "Yes," before explaining how he polls better than Clinton in certain head to head polls.
And the candidate's supporters have taken note, too.
When asked, a handful of Sanders supporters almost unanimously said they were confident in their candidate's electability, even if it wasn't a reason they were backing the Vermont senator.
"I doesn't concern me at all," Sean Dolstad, a graphic designed from Las Vegas, said bluntly, reflecting what many of his Sanders supporting brethren said on Wednesday.
Clinton supporters, on the other hand, said their candidate's electability was a top reason they were supporting her, especially given the state of the Republican field.
"It matters tremendously," said Linda Overbey, a union member from Las Vegas. "I want to win, because for me, Donald Trump is a moron."