With less than a month until the Iowa caucuses, the Democratic primary is heating up. And it's getting ugly.

A Bernie Sanders-Elizabeth Warren feud was to be expected eventually. Despite the two candidates' long-standing friendship, they're competing for the same progressive section of the Democratic electorate and need to differentiate themselves. But the subject of the fight itself — anonymous sources close to Warren leaking that Sanders told her he didn't believe a woman could beat Donald Trump in 2020 followed by Bernie categorically denying it — is surprising considering how civil, friendly, even, Warren and Sanders have been thus far in the race.

But the passionate (read: aggressive) response to the claim — complete with Bernie supporters spamming Warren's comment section with snake emojis — worries me a little. And it's not because I dislike Sanders (My primary vote is very much not committed), or think he's a sexist (his record on gender equality is pretty stellar), or think either candidate is lying. It's because increased tensions between the two most prominent progressive candidates can easily lead to more Democratic in-fighting than nuanced and useful debate over which direction the party should be taking.

Disagreeing on who the nominee should be is OK, good, even. There should be numerous viewpoints on something as momentous as a candidate who is going to have to defeat Donald Trump. However, when that debate becomes a fight, with two camps who should be on the same side imposing a morally absolutist view of primary right-and-wrong, it becomes an issue. It becomes an example of dangerous fractures in the Democratic Party.

And it becomes a chance for Donald Trump to win in 2020 the same way he did in 2016.

When Hillary Clinton won the nomination in 2016, plenty of Bernie supporters were, understandably, unhappy. But valid concerns over the direction of the party and the Democratic establishment were taken and turned into votes for Trump. One out of 10 Sanders supporters voted for Donald Trump in the general election, most out of a belief that Sanders' vision for the country was being unfairly ignored by typical Democratic politicians.

Sanders may well be on his way to clinching the nomination but regardless of if he does or not, the only way to ensure that a repeat of 2016 doesn't occur is get ALL Democrats, regardless of who they voted for in the primaries, to vote blue. A divided voter base is not an effective one, not in an election with this high of stakes.

The Warren-Sanders feud and the way supports of both candidates have responded to it makes me worried that this necessary unity might break. People should support who they want in the primaries, defend their chosen candidate, whatever — they should just remember that the stakes are much higher in November.