Since Donald Trump's stunning upset victory, Democrats have puzzled over how to flip some of the nearly 63 million Americans who cast their ballot for him in the 2016 election. Best-selling author and activist Naomi Klein believes the party would be better served by targeting a much larger demographic: Americans who didn't vote at all.

"You know, many of the people who voted for Trump in this electoral cycle—not all of them, but a good slice of them—voted for Obama in 2012 and 2008," Klein reminded Channel 4's John Snow, when asked how to "fire up the people" who voted for Trump.

"But," she added, "there are also millions and millions more Americans... who didn't vote at all. So, I think there needs to be a political project in the United States that is exciting, that reaches non-voters." 

Forty-five percent of American adults did not vote in the 2016 election, a 20-year high.

Confronted with two historically unpopular candidates, Republicans' superior turnout "probably" cost Clinton the election, reported FiveThirtyEight in January. According to the Guardian, "There are many reasons why [Americans] didn’t vote, but one takeaway is clear: the obstacles to voting disproportionately affect people of color."

"Trump's voters are not the most vulnerable in the U.S. economy," Klein added. "They're more in the middle, and the people who are really losing out don't have any political voice whatsoever."

Klein's new book, No Is Not Enough: Resisting Trump's Shock Politics and Winning the World We Need, was released in June.  

Watch: