"It's the economy, stupid."

US President Donald Trump's volatile leadership can be mystifying, but for those who support him, much of his appeal rests on his business boss persona.

When they voted for him, they were looking for a chief executive who would deliver prosperity, especially to inland America.

His record is imperfect in that election promises made to towns reliant on manufacturing haven't necessarily come to pass. But overall, unemployment is close to a 50-year low and the economy has grown strongly over the last five years.

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Mr Trump's approval rating is hazardously low for an incumbent, hovering in the low-40s, but it has remained steadfast. Experts say that it's the economy that's been keeping him there.

A CNN poll found that 26 per cent of those who approve of him do so because of the economy, which is more than double the next commonly given answer.

Which is why this week's appearance of the "inverted yield curve" is highly problematic for the administration.

And the President knows it.

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Much depends on when a recession strikes

Yield curve inversions preceded the last seven recessions.

The average and median lengths of time from inversion to the start of a recession are 15.1 and 16.3 months.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 32 seconds 32 s Wall Street suffers worst day of the year on recession fears

And guess what? The 2020 presidential election is roughly 15 months away. That could pose a big problem for the Trump campaign if the US economy is on the downward slide into election day.

The only sitting presidents who lost re-election in the last century did so after a recession hit.

They include Herbert Hoover in 1932, Jimmy Carter in 1980 and George H W Bush in 1992.

It was George H W Bush's loss to Democrat Bill Clinton that led to the colourful summation of what wins re-election.

Democratic campaign strategist James Carville smiled and said, "It's the economy, stupid."

The trade war with China could cloud consumer confidence

But there's another popular US axiom that's worth noting: "Vote one's pocketbook."

Voters may huff and puff about personality and ideology, but at the end of the day, they tend to choose a candidate they believe will help them financially.

When it comes to Mr Trump, people will tolerate a lot of things they don't like (think relentless tweeting and the use of polemic language around women, race and the like) for things they do (the anti-politician approach and a strong hand on the economic tiller).

Which brings us to the trade wars.

The President has long claimed that China and China alone would bear the costs of his increasing tariffs.

Yet on Tuesday, he conceded that US consumers could be affected by the trade war. It came in the form of an announcement that he'd delay some of the latest tariffs on $US300 billion in Chinese goods, until after the winter holidays.

"We're doing this for the Christmas season, just in case some of the tariffs would have an impact on US customers," Mr Trump said, before adding, "which, so far, they've had virtually none."

While some farmers and manufacturers have felt some effects, the tariffs have largely been out of sight, out of mind for US voters, amounting to roughly a 5 per cent tax rate on the total imports from China.

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As Mr Trump continues to ratchet up the tariff percentages and expand the number of goods affected, consumers will pay more in stores.

If voters look at their pocket book and determine they can't afford that Chinese-made toy for Christmas, they may start eyeing other candidates for commander-in-chief.

Could Democrats see a surge?

Democrats like Bernie Sanders and Elizabeth Warren have woven income inequality into their main campaign points, saying the middle class isn't feeling secure. They've proposed major structural change to healthcare, college finance and taxation.

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Signs of economic trouble could get voters thinking more about such progressive platforms. Though, if the primary election of 1992 (remember, the one that brought us "It's the economy, stupid"?) is any indication, voters might choose a safe, familiar path — a centrist candidate like Joe Biden.

Mr Trump has largely labelled the progressive's economic redistribution plans as "socialism".

So far, he's blamed the economy's perilous position on the federal reserve, China and the media. One Republican strategist told Bloomberg that if the economy continues to worsen, he'll highlight the Democratic drift toward "socialism" as the root cause.

In the end, it's the timing (stupid)

Currently, the administration argues that the Federal Reserve is compounding the problem by keeping interest rates higher than it needs to. They say that both encourages investors looking for a return from US Treasury Bonds at a time when rates are low in other countries and keeps a lid on domestic consumer spending.

The thing is, that like so many things in economics and politics, it's all about the timing.

The President has been able to fan the already accelerating US economy with tax cuts and pro-business policies since he came to office, stimulating job growth and consumer sentiment.

But his Chinese trade war comes at a time when global growth is slowing. Chinese unemployment is up; Brexit is creating uncertainty in the UK and Europe where large economies, like powerhouse Germany, are showing negative trends.

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Mr Trump's tariffs — and a global trade war, if that's the result — will further dampen turnover and confidence at the worst possible time, economically and politically. And in the end, it might cost him in 2020.