JPMorgan Chase & Co. strategists are starting to make forecast and strategy changes around the potential that President Donald Trump gets so overconfident in the robust economy and markets that he makes a "major miscalculation.'

US President Donald Trump has not been shy about taking credit for the robust US economy. Credit:AP

The worry is that "US economic and equity market resilience despite tariffs will embolden the President on all geopolitical fronts - autos, Nafta and particularly Iran - and thus risk a major miscalculation from sanctions that are tough to calibrate," strategists led by John Normand wrote in a note September 21.

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The strategists said that's part of the reason the firm has boosted oil-price forecasts, with a spike in Brent to $US90 a barrel "likely" on revised estimates of how much crude demand from Iran might drop as countries respect the US sanctions due to begin in November.