Paris, France - Donald Trump's former national security advisor John Bolton said the Republican frontrunner for the 2024 election simply "hasn't got the brains" to become a dictator.

Bolton, who worked for the Trump administration from 2018 to 2019 before turning into a fervent critic of his ex-boss, gave an interview to French newspaper Le Figaro, which was published earlier this week.

In it, the 75-year-old played down fears that Trump would pivot to full-blown dictatorship if he were to return to the White House in November.

"He hasn't got the brains! He's a property developer, for God's sake!" Bolton insisted.

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The long-time diplomat also pointed out Trump's extremely limited attention span and complete self-absorption.

"Everything is episodic, anecdotal, transactional" for the 77-year-old, Bolton said. "And everything is contingent on the question of how this will benefit Donald Trump."

In a new foreword to his 2020 book The Room Where It Happened, Bolton called Trump "unfit to be president" and suggested a second presidential term would be worse than the first.

With this year's election virtually guaranteed to be a rematch with President Joe Biden, Trump has ramped up the violent rhetoric against minorities and political rivals.

He has also given coy answers to questions over whether he intends to be a dictator, leaving open the possibility for "day one" of a new term.