The crystal ball for political pundits and activists, aggregated daily by RealClearPolitics.com, are the presidential polling numbers. They’re like TripAdvisor for travelers interested in a guided tour to a single destination: The White House.

This data, honed by habit and regurgitated as gospel, is used by pseudo prophets and oracles to forecast winners and losers. Trump’s up, Trump’s down. The Democrats can’t lose, the Democrats can’t win.

In reality, it just doesn’t matter.

That’s because in the cool recesses of the West Wing, only two numbers merit constant vigilance. One is the size of the audience commanded by our commander-in-chief for the greatest political reality show in history — easily 100 million a day between media coverage (TV, cable, print, online) and daily conversations around the dinner table.

Here’s the more telling number, one that history confirms is both the president’s greatest selling point and his best buttress against any of the more than 20 Democrats out to defeat him: the Dow Jones Industrial Average.

Created more than 130 years ago by Wall Street Journal editor Charles Dow and statistics savant Edward Jones, it drives every story line about America’s economic health and, by extension, our own.

Impacted by world events as much as economics (wars, unrest, disasters natural and manmade, etc.), the index consists of 30 corporate behemoths representing millions of jobs and trillions in value. It includes tech giants like Apple and Microsoft, consumer giants like Walmart and Proctor & Gamble, and financial giants like Visa and American Express in an American potpourri of business power.

The Dow is also something else: a reliable diviner of an incumbent president’s odds of re-election.

Going back to 1928, only three incumbents — Herbert Hoover, Jimmy Carter and George H.W. Bush — failed to win a second term. All three shared one thing in common: they ruled amid a recession. Hoover presided over the start of the Great Depression. Carter was felled by long gas lines and 18 percent interest rates. Bush couldn’t prevent a stagnant national economy from mitigating an unmitigated triumph in Operation Desert Storm.

All the others — from FDR and Eisenhower, to Reagan, Clinton and Obama — won a second term by putting the economy first.

Fast forward to 2019. Jobs are back, inflation is modest, consumer confidence is near historic highs, and the Dow is up -- more than 6000 points since the president’s inauguration.

This is Donald Trump’s “trump card” to disarm the doubters and neutralize the naysayers, an accomplishment he can trumpet without a megaphone because it speaks for itself.

So when he’s slammed for ribalding Tweets, or second-guessed for trying to disarm North Korea’s Kim Young Krazy via engagement, or assailed when the Chinese manipulate the yuan, the president has this ace up his sleeve.

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Consider the travails of other nations today that don’t have it as good.

Britain’s GDP has been battered by Brexit, down 3 percent already, with another 3 percent to come if Boris Johnson goes ahead (or goes rogue) with a “no deal” exit.

Hong Kong has been paralyzed by massive protests that are not only killing sales and investment but freedom itself.

Greece? The biggest peacetime recession in history.

Brazil? Some 13 million out of work.

South Africa? No jobs, no electricity, and short of water.

Venezuela? 13,000 percent inflation, and citizens rabid with hunger.

By contrast, the Dow is riding a wave of success this year:

• Microsoft is up 30 percent.

• Cisco’s stock has doubled in three years.

• Coca Cola has healthy growth across every major beverage line.

• Proctor & Gamble has double digit sales gains in everything from Crest and Pepto-Bismol to Tide.

So let the handicappers go wild parsing polls in search of peril and potential. Let the cheerleaders on the left foment havoc with the confidence of those in the middle and on the right.

Like many presidents before him, Trump keeps a close eye on the Dow, with fingers crossed the good times continue to roll. Despite some nervy moments Monday, the Dow closed Thursday above the 26,000 mark and was up for the week by mid-day Friday.

So here’s the prophecy. Should the Dow fall below 20,000 before November 2020, signaling recession, Trump will be in trouble.

If it stays between 20,000 and 26,000, gird yourself for a competitive campaign.

Yet if the brainchild of Messrs. Dow and Jones eclipses 26,000 by Election Day, Donald Trump will be on his way to a second term.

Adam Goodman is a national Republican media consultant based in St. Petersburg and the first Edward R. Murrow Fellow at Tufts University’s Fletcher School of Law and Diplomacy.