Paul Begala, a Democratic strategist and CNN political commentator, was a political consultant for Bill Clinton's presidential campaign in 1992 and was counselor to Clinton in the White House. He is a consultant to the pro-Hillary Clinton super PAC Priorities USA Action. The opinions expressed in this commentary are his.

(CNN) There were two enormous problems with Donald Trump's speech at the Republican National Convention: too much darkness, not enough inspirational personal biography.

First, the tone. If Trump needs a theme song he should consider the opening line of Simon & Garfunkel's "Sounds of Silence": "Hello darkness my old friend." This was one of the darkest speeches I have ever heard from a major party candidate. It's midnight in America.

Trump is blessed with truly impressive children and a gifted wife; they were the highlight of the convention. Indeed, the only person named Trump who gave a lousy speech was The Donald. He failed to build on their strong performances.

Donald Trump's America is fearful. Afraid of crime, afraid of terrorism, afraid of immigrants. His America is angry. Angry about political correctness. Angry about international trade. Angry with President Obama. And very, very angry about Hillary Clinton's candidacy.

Speaker after speaker at this convention excoriated Clinton. That's standard political fare. But Dr. Ben Carson compared her to Lucifer. Gov. Chris Christie called for her imprisonment. And one informal Trump adviser called for Clinton to be shot for treason. (The Secret Service is investigating that one.)

"Fear and loathing on the Campaign Trail" was a great book by the late Hunter S. Thompson, but it's a lousy campaign strategy. Americans want lift and loft, especially when they are anxious. In the depth of the Depression, FDR won with the song "Happy Days Are Here Again." Ronald Reagan, running in a recession, was a sunny optimist.

In another recession, my old boss Bill Clinton told his convention, "I still believe in a place called Hope." And with a crumbling economy and two mismanaged wars, Barack Obama had "the audacity of hope."

Optimism is central to the American character. A focus on the future, and an endless faith that we can make tomorrow better than today -- these are at the heart of the American dream.

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Trump should have read Ronald Reagan's 1980 convention address. Like all challengers, he hammered the incumbent. But unlike Donald Trump he spoke of a bold, optimistic country. In fact, Reagan's words that night in Detroit 36 years ago were a cautionary note about dark demagogues like Donald Trump:

"The American people, the most generous on Earth, who created the highest standard of living, are not going to accept the notion that we can only make a better world for others by moving backwards ourselves. Those who believe we can have no business leading the nation."

Donald Trump wants to move America backwards, but he couldn't even move his party to unite behind him. He misreads the American character if he thinks darkness and division are winning political themes.

Which leads me to the second major failing of Trump's speech: The absence of a personal narrative. Whether it was Lincoln's rail-splitting or Barack Obama's Kenyan-Kansan unity, character, as reflected in biography, is the ultimate issue in selecting a president.

When people select a legislator, from city council to the Senate, they go through a checklist of issues, and ask, "Who will represent me on the issues I care about?" But when we choose an executive -- especially president -- we ask more fundamental, existential, self-definitional questions, like, "If my spouse and I both die, which candidate would we want to raise our children?"

This is especially important for a candidate with high negatives. Going into the 1992 Democratic convention, voters knew Bill Clinton had been accused of dodging the draft and cheating on his wife. They knew he'd gone to fancy schools like Georgetown and Yale and Oxford. So, many of them connected those dots and concluded Clinton was a wealthy, entitled, spoiled rich kid who didn't know or care about the struggles of the poor and middle class.

So we created "The Man From Hope." We could not erase the dots folks already had, but we added more: His mother was widowed before he was born; he was for a time raised by his grandparents, who ran one of the few general stores in Arkansas that served African-Americans as well as whites; he faced down his abusive, alcoholic stepfather when he threatened his mother; he went to college on a scholarship, and turned down lucrative jobs back East to return to Arkansas to make it a better place.

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Trump's narrative arc is that he inherited a fortune, made even more, and married beautiful women while starring on a reality show. Perhaps he is satisfied with that, but voters want to know their president is one of them, that he, as President Clinton famously said, "Feels their pain."

As the Democrats prepare to gather in Philadelphia, here's a pro tip. The party that wins the White House is the one that is viewed as more unified and more mainstream. It's hard to be both at once.

You can unify around an extreme conservative or an extreme liberal, as the parties did under Barry Goldwater and George McGovern. And you can be in the mainstream, but if your party isn't unified you can be torpedoed by a fringe, as Al Gore was sunk by Ralph Nader.

Trump's divisive, dark and disastrous convention is an opening for Hillary Clinton and the Democrats. If they can come together, speak to the concerns of the forgotten middle class, campaign in search of, as Clinton has said, common ground instead of scorched earth, she will go a long way toward turning out the lights on Donald Trump's dark brand of politics.