The rhetoric from the Hillary Clinton camp has gotten much more nasty in recent days, as it often does in an unexpectedly close campaign this close to the first primaries.
Bernie Sanders fans shouldn't be surprised by this turn. After all, they are taking on the status quo, and the entrenched powers have no intention of just politely giving up. If Sanders wins Iowa and New Hampshire you an expect things to get a whole lot worse, and it'll be Democrats slinging the mud.
What's more, even if Sanders wins the nomination, it is likely that Democratic insiders will still be working to take him down.
How ugly and personal will it get?

I'd like to introduce you to a possible future for America, the British Bernie Sanders - Jeremy Corbyn.

Before I go any further, let me say that Sanders and Corbyn are not identical. Corbyn is far more radically leftist than Sanders.
That difference can be seen most starkly in foreign policy, where Sanders is only progressive in a relative sense. If it wasn't for the fact that every other 2016 presidential candidate is a bleeding-from-the-eyes war-hawk, the foreign policy of Sanders wouldn't look all that progressive.
Corbyn, on the other hand, is a true anti-nuke, anti-war, anti-imperialist politician.

That being said, the similarities between Sanders and Corbyn are striking. For example:

both men call themselves "democratic socialists"
both support universal health care
both have strong civil rights records
both have served many years in the legislative branch

...and that's just the start. I could go on, but I want to get to the point of this essay.
The two biggest things that Sanders and Corbyn have in common is a) they are both on the far left side of the mainstream, center-left party, and b) they both made a shocking rise to political prominence in 2015.
In Corbyn's case, he barely managed to get the minimum number of MP nominations required to run for the leadership position, yet won in a landslide.

No leader has ever won office with a larger mandate, nor with so little support from their MPs.

Sanders' victory, should he win, would be similar.

It is an amazing story. Everyone in a position to block Sanders’ campaign did everything they could to sabotage him.
Knowing that coverage is the essential oxygen of politics, the media mostly ignored him. By one measure, corporate media gave Trump 23 times more coverage than Sanders! On the few occasions when they spilled a little ink on Bernie, it was to insult him and his socialist politics.

In the case of Jeremy Corbyn, he already won the leadership vote for the Labour Party in September. So if Sanders were to complete his unexpected insurgency and win the Democratic nomination, we might take a look at Corbyn's reception within the Labour Party as a roadmap for what to expect in the coming months.

Glenn Greenwald has already gave us a glimpse of what might lie ahead, and it isn't pretty. What might surprise you is that the problem isn't the Tories. The problem is the neoliberals in the Labour Party.

For those who observed the unfolding of the British reaction to Corbyn’s victory, it’s been fascinating to watch the D.C./Democratic establishment’s reaction to Sanders’ emergence replicate that, reading from the same script....

Just as was true for Corbyn, there is a direct correlation between the strength of Sanders and the intensity of the bitter and ugly attacks unleashed at him by the D.C. and Democratic political and media establishment. There were, roughly speaking, seven stages to this establishment revolt in the U.K. against Corbyn, and the U.S. reaction to Sanders is closely following the same script:

STAGE 1: Polite condescension toward what is perceived to be harmless (we think it’s really wonderful that your views are being aired).

STAGE 2: Light, casual mockery as the self-belief among supporters grows (no, dears, a left-wing extremist will not win, but it’s nice to see you excited).

STAGE 3: Self-pity and angry etiquette lectures directed at supporters upon realization that they are not performing their duty of meek surrender, flavored with heavy doses of concern trolling (nobody but nobody is as rude and gauche online to journalists as these crusaders, and it’s unfortunately hurting their candidate’s cause!).

STAGE 4: Smear the candidate and his supporters with innuendos of sexism and racism by falsely claiming only white men support them (you like this candidate because he’s white and male like you, not because of ideology or policy or contempt for the party establishment’s corporatist, pro-war approach).

STAGE 5: Brazen invocation of right-wing attacks to marginalize and demonize, as polls prove the candidate is a credible threat (he’s weak on terrorism, will surrender to ISIS, has crazy associations, and is a clone of Mao and Stalin).

STAGE 6: Issuance of grave and hysterical warnings about the pending apocalypse if the establishment candidate is rejected, as the possibility of losing becomes imminent (you are destined for decades, perhaps even generations, of powerlessness if you disobey our decrees about who to select).

STAGE 7: Full-scale and unrestrained meltdown, panic, lashing-out, threats, recriminations, self-important foot-stomping, overt union with the Right, complete fury (I can no longer in good conscience support this party of misfits, terrorist-lovers, communists, and heathens).

Britain is well into Stage 7, and may even invent a whole new level (anonymous British military officials expressly threatened a “mutiny” if Corbyn were democratically elected as prime minister). The Democratic media and political establishment has been in the heart of Stage 5 for weeks and is now entering Stage 6. The arrival of Stage 7 is guaranteed if Sanders wins Iowa.

Some people in the Hillary campaign are already hinting at Stage 6.
It's interesting to note how while almost everyone in the news media and Labour Party establishment has turned against Corbyn, actual citizens and voters have done the opposite.

Almost every constituency party across the country we contacted reported doubling, trebling, quadrupling or even quintupling membership, and a revival of branches that had been moribund for years and close to folding...
The survey findings are borne out by Labour’s national figures, released to the Guardian in a break with party tradition of keeping them secret. Membership jumped from 201,293 on 6 May last year, the day before the general election, to 388,407 on 10 January.

What's more, most of the new members are young people and people who left in protest of the Iraq War.
It's being called the "Corbyn effect".

You can see this being duplicated in America, where young people are turning out for huge Sanders rallies despite his campaign not being covered by the news media, and the Democratic establishment being generally hostile.