CHICAGO — Donald Trump has revealed no secrecy or nuance about the case he will make against Kamala Harris over the next 74 days.

The former president says the current vice president is left-wing (“Comrade Kamala,” “much more liberal than crazy Bernie Sanders”). She’s a lightweight (“dumb,” “dumb”). She’s a fraud, defined only by her ambition, disconnected from ordinary Americans (“So I don’t know, is she Indian or black?” “What happened to her laugh?… That’s the laugh of a crazy person”).

On Thursday night, Harris accepted the Democratic nomination in just 40 minutes with a fluid, powerful and well-argued speech aimed at dismantling Trump’s caricature of her.

It is hard to imagine anyone who began watching the speech with an undecided but genuinely open mind — surely there are a few such people left in these agitated times? — ending it with the thought: You know, I understand what Trump meant.

Harris became the Democratic nominee only because of a spectacularly weak public performance by President Joe Biden less than two months ago during his debate with Trump. The format of an acceptance speech is, of course, very different. Yet Harris’ performance was the opposite in every way.

Harris confirmed, and almost certainly reinforced, the widespread perception left by recent national and swing-state polls that this is a transformed race. After the Democratic convention, Trump will face an urgent need to prevent Harris from delivering an equally effective performance at their scheduled debate on September 10.

In her biography, Harris said her values ​​were shaped by her early career as a prosecutor. This background was also reflected in her rhetorical tone: well-organized, clearly spoken, largely devoid of lyrical flights.

In substance, however, it seemed clear that Harris was not merely pursuing her case. The speech had a large and strategically important defensive dimension.

Rather than unveiling a decidedly left-wing agenda, Harris offered a constellation of priorities that unite most Democrats: protecting abortion rights, voting rights, and Social Security and Medicare. Even within this familiar terrain, she often struck notes that emphasized traditionalism and hardline. She boasted of having confronted drug cartels and predatory banks as a prosecutor and attorney general. She said she wanted a tax cut for the middle class, while arguing that Trump’s tax changes would give relief to the wealthy at the expense of others.

On national security, Harris seemed at pains to dispel any doubts that the nation’s first female president would be tough enough. “As vice president, I have confronted threats to our security, negotiated with foreign leaders, strengthened our alliances, and worked with our brave troops abroad,” she said. “As commander in chief, I will ensure that America always has the strongest, most lethal fighting force in the world.”

Knowing that Trump is intent on creating her own immigration crisis, she tried to turn the tide. She blamed him for rejecting a bipartisan border security bill because he wanted to solve a political problem instead of a policy solution, and vowed to revive and pass the measure.

Knowing that the war between Israel and Hamas threatens to divide her party, Harris — depending on one’s perspective — sought to find middle ground or obscure the issue with language that offered something both sides could relate to. She was equally impassioned when she said, “I will always stand up for Israel’s right to defend itself,” and when she asserted that she is part of the Biden administration’s efforts to ensure that “the suffering in Gaza ends and the Palestinian people can realize their right to dignity, security, freedom and self-determination.”

The most important part of Harris’s defensive agenda, however, was not about politics or policy, but about herself personally. A woman with a biography that some voters might find exotic — a daughter of a mixed marriage, from a liberal city in a liberal state — told her story in ways that made her approachable, familiar and reassuring.

There were hymns to a mother who “never lost her cool” and taught her daughters “never to complain about injustice, but to do something about it.” She described a close-knit community in California’s East Bay, “a beautiful, working-class neighborhood of firefighters, nurses and construction workers.” She described her patriotism this way: “Fellow Americans, I love our country with all my heart.”

There seemed to be an obvious logic to Harris’s policy of reassurance. She and her team apparently believe that avoiding attacks on her record or character is a necessary condition for directing her own attacks on Trump’s character and record.

She called Trump “a man who is not serious” but warned that the consequences of a second term would be “extremely serious.” There was virtually no point in the Democrats’ standard anti-Trump litany that she didn’t mention: his denial of the election and the Jan. 6 riots, his recent conviction on 34 felonies in New York, the civil case he previously lost in a sexual harassment case, his skepticism about the NATO alliance and his defense of Ukraine against Russian attacks, his alleged sympathies for Vladimir Putin and North Korea’s Kim Jong Un.

Earlier in her speech, Harris noted that as a government lawyer, “in my entire career, I have had only one client: the people.” She later backtracked to note that, given the Supreme Court’s rightward shift, Trump would face fewer checks and balances in a second term than he did in his first: “Imagine Donald Trump with no guardrails, and using the immense powers of the presidency of the United States. Not to improve your life, not to strengthen our national security, but to serve the only client he’s ever had: himself.”

A politician who can effectively fuse offensive and defensive policies in a single speech is a formidable threat. This gift was the essence of the success of Bill Clinton and Barack Obama. It was something that eluded Hillary Rodham Clinton at key moments in 2016. And it was something that Democrats concluded was impossible to imagine an aging Biden doing in 2024, despite his success in 2020.

After Harris’ speech, there’s little doubt that Trump and his campaign realize she’s changed the course of the campaign, and there’s little doubt that they’re busy thinking of ways to do it again.