If you're ever interested in what an ugly Democratic Party primary campaign looks like, I would suggest taking a look at this exchange between Bill Clinton and Jerry Brown in a 1992 debate. It starts with a softball lobbed at Brown about Clinton's electability that Brown turns into a vicious attack based on a now-forgotten scandal involving conflicts of interest in Hillary Clinton's legal work.

"He is funneling money to his wife's law firm," Brown says. "It's not only corruption, it's an environmental disaster and it's the kind of conflict of interest that is incompatible with the kind of public servant we expect for president of the United States." Brown goes on to say he would refuse to serve as Clinton's vice president. (This argument was somehow literally about chicken shit.)

Clinton's response: "I feel sorry for Jerry Brown." They go back and forth, with Clinton calling Brown dishonest and counterpunching with: "Jerry comes here with his family money and his $1,500 suit and his lying attacks."

Really. Watch it. It's amazing.

By some accounts, personal animosity between Brown (who staged a political comeback and is now once again governor of California) and Clinton have lingered for a quarter century. But, crucially, despite what was said at the time there was no problem unifying the party. Brown supported Clinton in November, Clinton easily carried California, and life went on.

This is crucial context to keep in mind while watching the Bernie versus Hillary campaign of 2016, which currently has many Democrats who aren't closely aligned with either candidate paranoid that the arguments will leave the loser's supporters embittered and unable to support the winner. The current race feels very vibrant right now to those who are emotionally and intellectually invested in the outcome, but by the standards of past campaigns, this Democratic primary season has been a remarkably bloodless affair with very little in the way of personal attacks or viciousness.

On the Democratic side, this has been a year of substantive fights about important policy issues with both candidates fundamentally approaching the answers from the left relative to the status quo. The differences between Clinton and Sanders are real and important, but they amount to an argument about whether to try to shift the country a little bit to the left or a lot to the left. Under the circumstances, it would be very odd for it to produce a lasting, unbridgeable divide if earlier elections have not.

2016 has been a low-key Democratic primary

Bernie Sanders started his 2016 campaign with a promise to run a positive, issue-oriented campaign. Like anyone else running for office, he has not entirely adhered to this. But he's come pretty close. His campaign is mostly about his big ideas — bank breakups, single-payer health care, free college, giant tax hikes, banning fracking, etc. — and his main slam on Hillary Clinton is simply that she isn't as left-wing as he is.

This is pretty clearly true, and it's generated a Democratic contest that is in some ways frustrating in its simplicity — Clinton and Sanders have been locking horns for months with nothing new to say.

It also feels unusually intense and vicious to many heavy consumers of internet news. Thanks to social media, lots of supporters of both candidates are now spending their free time acting as amateur advocates for their preferred campaign. This makes the race more intense and immediate than many past campaigns, and there has certainly been a lot of name-calling on Twitter.

But the actual campaign has been, by the standards of campaigns, remarkably issue-oriented and low-key compared to past races. A key flashpoint, for example, has been Clinton and Sanders wrangling over whether Sanders fully understands which sections of the Dodd-Frank Act authorize exactly which agency to break up banks under which circumstances.

2008 was full of mud-slinging

The ideological gaps between Clinton and Barack Obama were considerably smaller in 2008 than the Clinton-Sanders divide this year. But rather than leading to a kinder primary, it led to a more vicious one.

Clinton aides floated pictures of Barack Obama dressed in traditional East African garb, fanned the flames of rumors around a mythical tape of Michelle Obama ranting against whitey, and ran a major campaign ad alleging that Obama couldn't keep the country safe in the event of a crisis.

Obama ran an ad about how Clinton "will say anything" to get elected and "change nothing" if she wins.

His campaign's oppo research team also shopped considerably tougher hits against the Clinton Foundation's financial practices (see this story I wrote in 2007) than anything Sanders has dished this cycle.

Clinton's team bristles at the insinuations of corruption implicit in Sanders's attacks on her paid speaking appearances with Goldman Sachs, but even this is kid gloves stuff in the scheme of things. Her buckraking career is actually much more extensive than two talks for one bank, but Sanders maintains a relatively narrow focus because he really is obsessed with the specific subject of major banks' political influence, and the two candidates really do have a genuine disagreement.

2004 was fast but brutal

In retrospect, the 2004 Democratic primary can look like a cakewalk. John Kerry finished in first place in Iowa, trailed by John Edwards.

The two frontrunners left corn country to conduct a quick, statesmanlike campaign that showed Edwards had strength in the white South but that white Southerners were simply far too small a share of Democratic voters for him to prevail anywhere. The campaign was so respectful that Edwards seemed like an obvious choice to serve as Kerry's vice president from the beginning, and in many ways that seemed like the outcome Kerry was aiming for all along.

But the real story of the 2004 race came earlier, in the pre-Iowa phase dominated by the rise to prominence of Howard Dean.

Dean excoriated the Democratic Party's leadership in harsh terms, and led to outright panic and the desperate bid to recruit Gen. Wesley Clark into the race to create a non-Dean anti-war candidate. Independent expenditure groups supporting Dick Gephardt ran ads using Osama bin Laden imagery against Dean and Gephardt accused Dean of being against Social Security and Medicare.

What ended up happening was that Gephardt essentially committed a murder-suicide attack on Dean. He scared voters about the insurgent's electability but also rendered himself toxic, leading Iowans — and then Democrats more broadly — to embrace the above-the-fray Kerry.

Democrats will be unified in November

The overall trend is that primary campaigns are becoming kinder, gentler, and less personal in nature.

That reflects a two-fold transformation of party politics in which the Democratic Party has become more ideologically homogenous while Democratic Party voters have become better-educated and more ideological. In the multi-candidate field of 2004, voters ended up punishing candidates who dished out tough hits. In the two-person race of 2008, both campaigns found themselves torn between wanting to slam their opponent and wanted to avoid backlash for doing so. By 2016, you have Sanders and especially Clinton treating the other candidate with kid gloves. Both campaigns know that despite the vicious Twitter wars, there's no ideological chasm between Clinton supporters and Sanders supporters and everyone prefers a respectful campaign.

This all means that far from having an unusually difficult time unifying the party, once the campaign is over Clinton should have an unusually easy time.

Sanders's run against her has been overwhelmingly focused on the issues. And whatever you think of Clinton's stances on taxes, Wall Street regulation, subsidizing college tuition, or expanding public sector health programs, there's absolutely no doubt that she and Sanders are pulling in the same direction while all Republicans are pulling the other way. There's no chicken-related corruption charges or allegations of secret adherence to Islam that transcend or disrupt the basic left-right partisan framework — just a simple, sincerely felt disagreement about how expansive an agenda it makes sense to run on.