President Donald Trump in the Diplomatic Room of the White House in 2017 (Joshua Roberts/Reuters)

But that attitude may mean they'll be burned again.

About every other year, I make it a point to stop by Netroots Nation, the annual gathering of thousands of progressive activists, to take the temperature of the American Left. One year, I was even invited to join a panel, and I enjoyed jousting with attendees while playing the role of piñata at their party.

This month, Netroots Nation met in Philadelphia. The choice was no accident. Pennsylvania will probably be the key swing state in 2020. Donald Trump won it by only 44,000 votes or seven-tenths of a percentage point. He lost the prosperous Philadelphia suburbs by more than Mitt Romney did in 2012 but more than made up for it with new support in “left behind” blue-collar areas such as Erie and Wilkes-Barre.

You’d think that this history would inform activists at Netroots Nation about the best strategy to follow in 2020. Not really. Instead, Netroots events seemed to alternate between pandering presentations by presidential candidates and a bewildering array of “intersectionality” and identity-politics seminars.

Senator Elizabeth Warren pledged that, if elected, she would immediately investigate crimes committed by border-control agents. Julian Castro, a former Obama-administration cabinet member, called for decriminalizing illegal border crossings. But everyone was topped by Washington governor Jay Inslee. “My first act will be to ask Megan Rapinoe to be my secretary of State,” he promised. Naming the woke, purple-haired star of the championship U.S. Women’s Soccer team, he said, would return “love rather than hate” to the center of America’s foreign policy.

It is true that a couple of panels tried to address how the Left could appeal to voters who cast their ballots for Barack Obama in 2012 but switched to Trump in 2016. “How’d we lose the working class? Ask yourself, what did we do for them?” asked Rick Smith, a talk-show host who explores labor issues, adding:

You called them stupid. You marginalized them, took them for granted and you didn’t talk to them. For 20 years, the right wing has invested tremendous amounts of money in talk radio, in television, in every possible platform to be in their ears, before their eyes, and on their minds. And they don’t call them stupid.

But that kind of introspection was rare at Netroots Nation. Elizabeth Warren explicitly rejected calls to keep Democrats from moving too far to the left in the next campaign: “The progressive agenda is America’s agenda, and we need to get out there and fight for it!”

Warren and her supporters point to polls showing that an increasing number of Americans are worried about income inequality, climate change, and America’s image around the world. But are those the issues that actually motivate people to vote, or are they peripheral issues that aren’t central to the decision most voters make?

Consider a Pew Research poll taken last year that asked respondents to rank 23 “policy priorities” from terrorism to global trade in order of importance. Climate change came in 22nd out of 23.

There is a stronger argument that Democrats will have trouble winning over independent voters if they sprinting so far to the left that they go over a political cliff. As my NR colleague Ramesh Ponnuru wrote last month in the New York Times:

On several polarizing issues, Democrats are refusing to offer the reassurances to moderate opinion that they once did. They’re not saying: We will secure the border and insist on an orderly asylum process, but do it in a humane way; we will protect the right to abortion while working to make it less common; we will protect gun rights while setting sensible limits on them. The old rhetorical guardrails — trust us, there’s a hard stop on how far left we’ll go — are gone.

Many leftists acknowledge that Democrats are less interested than they used to be in trimming their sails to appeal to moderates. Such trimming is no longer necessary, as they see it, because the changing demographics of the country give them a built-in advantage. Almost everyone I encountered at Netroots Nation was convinced that President Trump would lose in 2020. Earlier today, Roland Martin, an African-American journalist, told ABC’s This Week, “America is changing. By 2043, we’ll be a nation [that’s] majority people of color, and that’s — that is the game here — that’s what folks don’t want to understand what’s happening in this country.”

It’s a common mistake on both the right and the left to assume that minority voters will a) always vote in large numbers and b) will vote automatically for Democrats. Hillary Clinton lost in 2016 in part because black turnout fell below what Barack Obama was able to generate. There is no assurance that black turnout can be restored in 2020.

As for other ethnic groups, a new poll by Politico/Morning Consult this month found that Trump’s approval among Hispanics is at 42 percent. An Economist/YouGov poll showed Trump at 32 percent among Hispanics; another poll from The Hill newspaper and HarrisX has it at 35 percent. In 2016, Trump won only 29 to 32 percent of the Hispanic vote.

Netroots Nation convinced me that progressive activists are self-confident, optimistic about the chances for a progressive triumph, and assured that a Trump victory was a freakish “black swan” event. But they are also deaf to any suggestion that their PC excesses had anything to do with Trump’s being in the White House. That is apt to be the progressive blind spot going into the 2020 election.