Here, Donald Trump claims that President Obama is suffering from some type of mental illness. In the tweet, he even referred to his predecessor as a 'psycho!'.
Experts in mental health and neurology regularly claim that Trump is suffering from a cluster-B personality disorder, in addition to possible neurological decline.
[Trump] is not so much a Narcissistic personality as a Cluster B character type. Those with the character flaws that fit a Cluster B profile are interested only in their own self-aggrandizement, disregarding the need for stability, and with little care for the greater good – regardless of how much they claim to do so***. They enjoy creating conflict as opposed to dealing with conflict. While I hope this is never the case we can very likely find ourselves in an administration that inadvertently pours more fuel on fires around the world rather than attempting to extinguish them.*
Trump's neurological decline has received a lot of attention as well.
Research has shown that changes in speaking style can result from cognitive decline. STAT therefore asked experts in neurolinguistics and cognitive assessment, as well as psychologists and psychiatrists, to compare Trump’s speech from decades ago to that in 2017; they all agreed there had been a deterioration, and some said it could reflect changes in the health of Trump’s brain.
A doctor spoken to by Stat stated the following:
John Montgomery, a psychologist in New York City and adjunct professor at New York University, said “it’s hard to say definitively without rigorous testing” of Trump’s speaking patterns, “but I think it’s pretty safe to say that Trump has had significant cognitive decline over the years.”