Hillary Clinton’s legendary perseverance and resilience are on full display in 2016. She is winning the Democratic nomination despite a mile-high wall of personal attacks. It is exactly why she is the best candidate to take on Donald Trump.

Bernie Sanders has done many things right in this race — and one thing very wrong. It is the wrong decision that I believe partially accounts for his poor showing on March 15th.

Let’s start with what’s right about Bernie’s message: he is a passionate purveyor of core progressive principles who has activated and energized millions of young voters. He speaks with conviction about crucial issues and he has helped bring those issues to the fore in 2016.

Here’s what’s wrong, terribly wrong: He caved to the pressure from his campaign manager Jeff Weaver and top aide Tad Devine to ride the ever-present wave of Hillary hate and to go after her character, impugning her honesty and insinuating that she is untrustworthy.

As I’ve argued repeatedly, Bernie’s Wall Street dog whistle is a barely concealed attempt to accuse Hillary Clinton of corruption, despite the fact that he lacks a scintilla of evidence to support that claim. No matter how lofty and inspiring his message, it is deeply unjust – and frankly, reckless – to run a campaign premised on the destruction of Hillary’s character through false innuendo. Especially when Democrats are facing a dangerous opponent like Donald Trump in a general election.

At some point in late 2015, Bernie’s campaign message and the behavior of his supporters became less about something and more against someone. Bernie’s campaign team determined that his path to victory runs right through Hillary’s integrity.

Tad Devine, Jeff Weaver, Cornel West, Killer Mike, and other Bernie aides and surrogates have led the charge against Hillary’s character, calling her honesty into question with no justification or evidence.

It has been a grave mistake for his candidacy, perhaps fatal. You can’t spend 2015 promising to run a positive, issue-driven campaign, then pivot in 2016 to a full-bore character attack against Hillary Clinton.

Going forward, it would be unwise for Hillary’s supporters to pressure Bernie to drop out, despite the prohibitive delegate math. All we should ask is that he drop the character attacks and stay positive.

And he should let go of this outlandish strategy:

Bernie Sanders is falling further and further behind in pledged delegates — but even after Hillary Clinton’s Tuesday romp, his campaign says there’s a longshot strategy that lets him regain momentum and win the Democratic nomination by relying on superdelegates even if he comes into the Philadelphia convention still trailing Clinton.

Bernie’s campaign aides, surrogates and supporters have criticized the superdelegate system, claiming it reflected an antiquated structure that unfairly favored the “establishment” candidate. What they haven’t admitted is that Tad Devine helped craft that system and that Bernie himself is a superdelegate. Either way, the superdelegates will not save Bernie’s campaign.

Hillary is winning and she’s winning because of her positive, pragmatic and uplifting message. Bernie could learn a thing or two from her campaign.

UPDATE: Hillary’s chief strategist provides more context on what went wrong for Bernie Sanders:

His campaign decided to be increasingly negative and increasingly explicit in assailing Clinton. The negative strategy backfired. The question will be, will he return to a tone that is more issue-focused, rather than attack-based?