After a long, divisive battle, can Dems really unite behind the last woman standing?

After an aggressive New York primary campaign Bernie Sanders and Hillary Clinton were supposed to go back to being friendly. Or they were, at least, meant to hide their disdain for one another better.

That didn’t happen.

Just a few days after Sanders’s major defeat in New York and his trip home to Vermont so that he could “recharge his batteries” he was back out there criticizing Clinton for her poor judgment. And Clinton’s team was floating names of potential V.P. picks for her and focusing on Donald Trump, a clear signal to the Sanders campaign and his voters that the primary is all but over.

This has only angered Sanders’s supporters even more. Over the weekend, Sanders surrogate and actress Rosario Dawson said that she felt solidarity with Monica Lewinsky because both had been bullied by the Clinton machine. Sanders didn’t support her statement, but he didn’t disavow it either.

And though the battle continues to rage into Tuesday’s primaries where Clinton is poised to expand her delegate lead, it’s not actually the war of words between the campaigns that’s the issue. It’s unification.

The clearest and most obvious obstacle to unification for the Democrats is that Sanders’s supporters don’t like Hillary Clinton all that much. Surveys have shown that as many as 25% of Sanders voters wouldn’t vote for Clinton in the general election. That’s compared to just 14% of Clinton’s voters who say they wouldn’t get behind Sanders if he was the nominee.

And then there’s the faction of Sanders supporters who say they’ll be voting for Donald Trump instead of Clinton. They see their positions on free trade and the economy more generally as pretty aligned. This is only bound to increase after Trump said last week that he wants to raise taxes on the wealthy. I’m sure that led to a collective groan at Clinton HQ.

We’ve been here before. In May 2008, Indiana exit polls found that 50 percent of Clinton supporters said they’d stay home or vote for McCain rather than vote for Obama and we know that they turned out for him at the general election. But that doesn’t mean that this is any less troubling as Democrats look ahead to November.

Democrats are also facing a serious ideology obstacle on their path to winning in November. Bernie Sanders isn’t a Democrat, he’s a socialist. He’s very open about it and we all know that he’s only running as a Democrat because an Independent candidacy would be dead in the water.

But what establishment Democrats didn’t bank on was how many Americans would identify with socialism. A recent poll found that 57% of Americans think that socialism “has a positive impact on society.” We know the Democrat electorate is becoming more and more liberal, but that finding shocked everyone. Furthermore, as we know that Democrats and socialists have clear ideological differences, there will be no tradition of party unity here. This reality inevitably complicates matters for Clinton in get a fractured party to coalesce around her.

Then there’s her opponent to worry about. If it’s Donald Trump – and all the evidence suggests that it will be – she’s going to have a steep challenge in that he has shown an ability to bring in Independent voters and, critically, some Democrats, too. Some of this can’t be avoided in that Trump’s candidacy will always defy the odds, but Clinton needs a real progressive running mate to keep the Obama coalition together as best she can.

By now we’ve all seen the list of 10 or so names that the Clinton campaign is considering as VP and they all offer great qualities she’d want in a running mate. That said, I believe that Ohio Senator Sherrod Brown is the best choice of a running mate. He’s been a longtime Clinton ally who is more progressive than she is. He’s universally respected and well liked. And he brings with him Ohio, a valuable swing state that she’ll need to capture the presidency.

Tuesday’s results will shed some light on how much longer Sanders is going to stay in the race. Though he’s said that he’s staying in until the end, there are rumblings that his campaign will reevaluate after Tuesday. But even if he does exit the race – and I don’t think he will – Clinton has her work cut out in unifying this Democrat party. Sanders will have to play a role himself and Elizabeth Warren will have to come off the sidelines. And Senator Brown will be a huge asset to her as she woos Sanders’s backers.

Who knew we’d still be fighting socialism in 2016?