Doctor and psychiatrist Carol Lieberman says President Biden's behaviour could be a sign of "dementia".

She told GB News: "I've actually written an open letter asking him to take a mental competency test. Because I do this as an expert witness, I do cases regarding competency, and he certainly would fail.

"There's no way that he would pass even the baseline, the preliminary mental competency test. And I would then send him to a neurologist and have him be given all kinds of neurological tests, PET scans, CAT scans, lots of cardiovascular tests because he had a brain bleed years ago. He had an aneurysm and a brain bleed.

"And he's on medication now for a cardiac arrhythmia that can cause transient ischemic attacks. So I think Alzheimer's is the most common dementia. And then comes vascular. But I think because of his vascular history, it's important to look into that first."