On Oct. 28, 1980, in the final debate of his race against Jimmy Carter, Ronald Reagan asked a question that has come to define presidential politics.
"Next Tuesday all of you will go to the polls, will stand there in the polling place and make a decision," Reagan said. "I think when you make that decision, it might be well if you would ask yourself, are you better off than you were four years ago?"
The answer for most voters was no, and Reagan won the election with 489 electoral votes to Carter's 49.
The question, or some close variation of it, has popped up many times since. "Are you better off than you were four years ago?" asked Bill Clinton in 1992. (In 1996, seeking re-election, Clinton declared, "We are better off than we were four years ago.")
"Are you better off than you were four years ago?" asked Barack Obama in 2008.
It worked for Clinton, and it worked for Obama. Now, the question is whether it will work for Donald Trump.
The president's Democratic 2020 challengers face a daunting problem: Unless there is a serious economic downturn, the answer to the are-you-better-off question will work in the president's favor, not his opponent's.
The unemployment rate, 3.7%, is the lowest it has been in half a century. June's employment report -- 224,000 new jobs -- brought another strong performance. The economy is growing at a slightly better than 3% annual rate. Most important, in the context of an election, wages have grown 3.1% over last year with low inflation -- improvement that has not been seen in years.
Any commentary on the 2020 election should include the warning that things could change. But barring a significant reversal, in 2020 most voters would likely answer yes when asked if they are better off than they were four years ago. And then they would vote to re-elect the incumbent president.
That leaves Democrats with the task of convincing millions of Americans to vote against their economic interests, to choose a Democrat over the president, during a time of economic satisfaction.
How to do it? Some Democrats have chosen to argue that there is something so wrong with the president -- he's a racist, or he is an agent of Russia, or he is something equally terrible -- that the traditional measures of a successful presidency do not apply.
Look at Democratic front-runner Joe Biden's entry into the race. Biden's announcement video focused entirely on the August 2017 white supremacist rally in Charlottesville, Virginia, in which a counter-demonstrator was murdered.
"We are in the battle for the soul of this nation," Biden said. "If we give Donald Trump eight years in the White House, he will forever and fundamentally alter the character of this nation -- who we are -- and I cannot stand by and watch that happen."
Fast-rising Democratic contender Kamala Harris chose another approach. "I know predators," the former prosecutor said recently, "and we have a predator living in the White House."
Other Democrats have portrayed Trump as a threat to American values, a threat to the rule of law, and a threat to the "norms" that guide our politics and lives.
Together, the message could be characterized as: Yes, the economy is growing, unemployment is low, and wages are rising. But America under a re-elected Trump would become a racist dystopia in which all the beliefs Americans hold near and dear would be under constant siege. How could any decent person vote to re-elect the president?
Beyond that, Democrats hope educated voters will be susceptible to anti-Trump social pressures, to being shamed out of voting for the president. The idea is that those voters will focus on their objections to the way Trump has conducted himself in office -- the tweets! -- and not on the economic results of his presidency. Indeed, a number of polls have shown that a significant group of voters who are happy about the economy still plan to vote against Trump.
"Trump's tenure is straining one of the most enduring rules in presidential politics: the conviction that a strong economy benefits the party holding the White House," wrote analyst Ron Brownstein in The Atlantic. "Across many of the key groups in the electorate, from young people to white college graduates, Trump's job-approval rating consistently runs at least 25 points below the share of voters who hold positive views about either the national economy or their personal financial situation."
Of course, Democrats can't ignore the economy. So far, when they have addressed it, they haven't been terribly creative, relying on the standard-issue Democratic critique of Republican presidents -- that Trump is creating an economy that benefits only his rich friends.
"Who is this economy really working for?" asked Elizabeth Warren at the first Democratic debate. "It's doing great for a thinner and thinner slice at the top."
It's not clear how well that will work. As The Wall Street Journal editorial board pointed out recently, under Trump, "wages are rising at the fastest rate in a decade for lower-skilled workers, and unemployment among less-educated Americans and minorities is near a record low." The result of the president's policies, the Journal argued, "has been faster growth and less inequality."
Another way to say that is that millions of Americans are better off than they were four years ago. The question in 2020 will be whether that matters.