Presumptive Democratic presidential nominee Hillary Clinton in Orlando on July 22. (Andrew Harnik/Associated Press)

“THE LAST thing we need,” Hillary Clinton said the day after the Republican convention ended last week, “is somebody running for president who talks trash about America.” With that, the presumptive Democratic nominee signaled that her party will offer a very different picture of America at its convention in Philadelphia this week — and rightly so.

The Democratic convention is likely to look and sound different in many ways from the one that just closed in Cleveland. The sea of white faces that television viewers saw on the GOP convention floor — there were fewer than 20 African Americans among the 2,472 delegates — will be replaced by a crowd that looks more like the diverse America of 2016. We hope we won’t hear chants calling for the imprisonment of the Democrats’ political opponents, or speeches suggesting that Donald Trump is somehow responsible for the acts of murderers, or has a pact with the Devil.

The contrast that’s most needed, however, is in how Ms. Clinton and her supporting cast assess the state of the nation as this momentous election approaches. Mr. Trump and the Republicans drew a dark portrait of an American dystopia, a blasted land paralyzed by violent crime, terrorism, killings of police, out-of-control illegal immigration and a “rigged” political system. It is, as we have said, a story that draws on painful disruption in parts of our society. But in whole and in detail, it is a lie. Part of what Democrats must do in Philadelphia, for the good of the nation and for the good of their party, is present a more balanced view.

Given the anti-establishment mood in much of the electorate, and polls showing deep discontent with the direction of the country, Ms. Clinton might have been briefly tempted to let Mr. Trump’s bleak rhetoric stand — to present herself as the candidate more able to manage a dangerous and turbulent time. Certainly, it is important to acknowledge and address legitimate anxieties raised by such events as the terrorist attack in Orlando and the recent shootings by and of police.

It is even more essential, however, that Americans be presented with the facts that belie Mr. Trump’s fear-mongering rhetoric. The U.S. murder rate is not soaring; in fact, it is at a historic low not seen since the early 1960s. Immigrants are not pouring across the southern border: Between 2009 and 2014, 140,000 more Mexicans returned to their country than migrated to the United States. Police officers are not being killed in record numbers; in fact, the number of police deaths has decreased in the past two decades. In short, the United States that Mr. Trump claims “I alone can fix” simply does not exist.

Ms. Clinton should recognize in her convention speech the very real pain some Americans are suffering. She should — and this would be another contrast with Cleveland — offer actual, substantive proposals to help spur growth and alleviate economic and social inequality. She should talk about the importance of both law enforcement and criminal-justice reform.

But she also should speak truthfully about the generally peaceful and prosperous country she is seeking to govern. It remains, as she said Friday, “the strongest, best-positioned country in the world for the 21st century.” It is not, as Mr. Trump insists, “a hellhole” — and it is not in need of a strongman.