Barack Obama - AP

Barack Obama urged Americans to defend democracy in a speech to the Economic Club of Chicago in which he appeared to use the rise of Adolf Hitler as a warning against the rise of bigotry and nativism under President Donald Trump.

Although he did not refer to Mr Trump by name, it brought accusations that a former president was comparing the current president with one of the most reviled leaders in history.

In the speech on Tuesday, Mr Obama told his audience that the danger was of “grow[ing] complacent”, according to Crain’s Chicago Business newspaper.

“We have to tend to this garden of democracy or else things could fall apart quickly,” he said during a question and answer session.

Despite the democracy of the Weimar Republic, he added, Adolf Hitler rose to power.

Obama went on an unhinged rant comparing Trump to Hitler and implied that Americans should vote Dem. or millions of people would be killed.

Bizarre remarks were made during an Economic Club of Chicago event on Tuesday night but have been largely ignored by the mainstream media.

— Katarina-Bot-Covfefe (@Welly_World) December 7, 2017

"Sixty million people died. ... So, you've got to pay attention. And vote," he said, referring to the death toll from the Second World War.

Critics of Mr Trump accuse him of fuelling nationalist and nativist feelings across the US and of stoking anti-Muslim rhetoric.

However, Mr Obama’s comments were seized on by the president’s supporters. Some said they were “unpatriotic” or pointed out that Mr Trump was promising to move the US embassy to Jerusalem, suggesting comparisons with a Nazi leader who ordered the Holocaust were nonsensical.

Adolf Hitler

Michael Johns, a Tea Party founder, described the comments as "absurd".

"It's unfortunate that a former president, who is no doubt an intelligent man, would make that mistake. Hitler killed six million innocent civilians; Donald Trump has created over one million jobs and killed absolutely no-one.

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"There is no equivalence."

He added that the words were symptomatic of America's growing political divide and the difficulty of communicating across party lines.

Jesse Watters, a political commentator, said on Fox News: "I thought Obama was better than this. To compare his successor to Adolf Hitler... horrible. It’s demeaning and beneath him.”

President Donald Trump Credit: AFP

He added that Mr Obama was bitter as his legacy being unravelled.

“I understand why he’s angry but that was a horrific comparison,” he said.

The row is a reminder of the dilemma faced by Mr Trump’s opponents on the Left. While they frequently talk up the dangers posed by his presidency, they run the risk of being accused of exaggeration if they cite lessons from Nazi Germany.

In June, North Korean state media likened Donald Trump to Adolf Hitler and compared the US president's "America First" policies to Nazism.

An editorial published by the Korea Central News Agency said Mr Trump's strategy towards the Korean Peninsula was "based on Hitler's dictatorial policies that separate people from their peers, justifies oppression and creates an atmosphere of fear in American political, social, media and information circles".