This chart may be the one that determines if Trump is re-elected in 2020

We're still a long way from President Donald Trump's 2020 re-election campaign, but with both Democrats and Republicans on edge about whether Trump can win again, it's never too early to start looking at his chances.

While most people focus on his approval rating, the best metric for determining Trump's odds of winning a second term may come from looking at consumer confidence in the economy.

In a presentation given at CNBC this week, political strategists Sara Fagen and Doug Sosnik demonstrated that consumer confidence, as measured by the Conference Board, has given indications, going back to Jimmy Carter's presidency, about whether presidents can win a second term.

As you can see in the charts below, when consumer confidence dipped during the third quarter of the third year of a president's first term, the president lost his re-election bid. If consumer confidence rose during the same period, the president was re-elected.

There's a lot of other issues hanging over Trump, so this metric may not hold up. But, if you're looking for a different metric to gauge Trump's future, this might be the one to watch.

Carter and Bush 41, for example, saw consumer confidence fall ahead of their failed re-election bids:

On the other hand, Presidents Barack Obama, George W. Bush, Ronald Reagan and Bill Clinton benefited from stable or rising levels of consumer confidence in the months leading up to their successful re-elections to a second term.

For now, consumer confidence seems to be working in favor of Trump's possible re-election bid.

Trump entered office with consumer confidence high at the end of the Obama administration, and it has only risen since. The Conference Board's present situation index has hovered around 160 in recent months, significantly higher than it was at the same time in the administrations of every president dating back to Carter.

That should set Trump up well in the minds of some voters — if current trends hold through the fall of 2019. But the strong economy has not helped Trump much so far: he has endured a poor approval rating of roughly 40 percent throughout his time in office.

A mounting trade war with key U.S. economic partners and ballooning budget deficits are among the factors that could derail any economic improvements seen during the early parts of Trump's presidency.

Perversely, if this metric holds up for Trump, Democrats desperate for Trump to be voted out of office may have to root for an economic recession, which runs counter to their own personal fortunes.

Here are the consumer confidence numbers for all presidents' first terms since Carter. Click on a color to highlight.

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