WASHINGTON

While President Donald Trump’s base is already fired up to vote in November, Democrats spent last week’s Democratic National Convention just trying to get a fire started.

Much of the Joe Biden convention was an exercise in base mobilization. There’s a reason for that. A Post-ABC News poll on the eve of the convention showed that while 65% of Trump supporters say they are “very enthusiastic” about supporting the president, only 48% of Biden supporters say the same about the former vice president.

Biden has an enthusiasm problem with two key constituencies he needs to win — younger voters and African Americans. Only 25% of voters aged 18-39 are “very enthusiastic” about voting for him. And CNN reports that Biden’s support among black voters is currently smaller than Clinton’s was in 2016. Worse, only 68% of African Americans aged 18 to 29 say they intend to vote for Biden — 17 points fewer than supported Clinton four years ago.

If you think Democrats are confident these voters will turn out, count how many times they urged viewers to “make a plan” to vote. An energized base doesn’t need that kind of encouragement.

Those efforts at base mobilization came at a cost. There was virtually no effort to win back the working-class voters who voted twice for Barack Obama but defected to Trump in 2016. The reason Trump is president today is because about one-third of the nearly 700 counties that twice voted for Obama went for Trump in 2016. According to Nate Cohn of the New York Times, Trump won because he “flipped millions of white working-class Obama supporters to his side.” If you were a working-class Obama-Trump voter watching this week’s convention, you heard a lot about gun violence, racial justice, and climate change, but not much directed at you. The message you heard was: Democrats are not interested in your support.

That showed in Biden’s acceptance speech. It was in many ways an impassioned and effective address. But not a word about the opioid epidemic and deaths of despair that are destroying their families. Not a word about the outsourcing of jobs that has decimated their communities. Not a word about confronting China, the country that unleashed COVID-19 on our country and has decimated many economic sectors with unfair trade practices.

Biden blamed Trump for the job losses from the pandemic. But these voters remember that before the pandemic hit, America had recovered half-a-million manufacturing jobs under Trump after losing almost 200,000 factory jobs in the Obama-Biden years.

Trump understands this, which is partly why just hours before Biden’s address, he held a rally in the former vice president’s birthplace, Scranton, Pennsylvania. “Joe Biden is no friend of Pennsylvania,” Trump said. “He’s actually … your worst nightmare. Biden supported every single globalist attack on Pennsylvania workers: NAFTA, China’s entry into the World Trade Organization, which built China into a power, TPP, Korea, the horrible, ridiculous Paris Climate Accord, which stripped our nation of its energy, and the so-called Clean Power Plan.”

Trump is behind in most battleground states polls, but the race in pivotal Pennsylvania has tightened. In July, Biden had an 11 point lead in the Fox News poll; a new poll this week shows Trump within the margin of error.

Trump now has the opportunity to do what Biden did not: use his convention to reach beyond his base, and make a pitch to the 10% to 15% of voters who have said they approve of his economic policies but don’t approve of him. It is in their economic self-interest to give him a second term.

Trump needs to give them permission to vote in their self-interest. To do that, he needs to acknowledge his flaws, and the fact that his brash New York approach sometimes rubs people the wrong way. His message should be: Despite my imperfections, I’m fighting for you. With that approach, he can keep his base energized and expand it at the same time. His convention is the place to start.

Follow Marc A. Thiessen on Twitter, @marcthiessen.