US President Joe Biden‘s critics have latched onto a video purportedly showing him falling asleep during the COP26 summit to rake up the 78-year-old’s alleged lack of mental and physical capacity to hold office. Biden was among several world leaders who spoke at the UN climate change conference in Glasgow, Scotland, on Monday. In the one minute, 19 seconds long clip, first posted to Twitter by a journalist, Biden can be seen shutting his eyes a few times as he listens to a speech at the conference. He is then approached by an aide and opens his eyes and continues listening to the speech.

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According to multiple media reports, Biden was listening to a pre-recorded message from South African disability rights activist Eddie Ndopu when he shut his eyes for around 20 seconds.

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“Biden appears to fall asleep during COP26 opening speeches,” wrote The Washington Post reporter Zach Purser Brown while sharing the video on Twitter, where it has racked up over 4.6 million views in less than 24 hours.

Joe Biden, 78, is the oldest person to serve as president of the United States with critics saying he is mentally and physically unfit for such a high-pressure role at this age. Former US President Donald Trump nicknamed Biden “Sleepy Joe” during the 2020 presidential campaign, and used COP26 footage to attack his successor again.

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“Biden went to Europe saying Global Warming is his highest priority, and then promptly fell asleep, for all the world to see, at the Conference itself. Nobody that has true enthusiasm and belief in a subject will ever fall asleep!” the New York Post quoted Trump as saying.

However, some on social media said Biden was just resting his eyes for a few seconds.

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Speaking during the summit on Monday, Biden urged fellow world leaders to take swift action to combat climate change.

Around 120 world leaders and thousands of delegates are attending the COP26 climate talks that will last till November 13.