This isn't anything new or different. Trump has not changed one bit since he came down the "golden escalator" to his bought crowd and called Mexicans "rapists", hell, he hasn't changed since before then. The only thing that has changed is that the stakes are higher and the spotlight is much brighter.
Many presidents and other politicians have a learning curve. They make some "rookie" mistakes. Then they learn, at least to keep their mouth shut so as to not exacerbate the situation. This guy has shown, from day ONE, that he is self destructive, that he doesn't learn, that he doesn't care to learn, and the only reason that he is still in office and not in a jail cell is that the ENTIRE GOP has aided and abetted him in order to retain power. There has been NO change since he was a candidate nor since he has been in office. As I said, the only thing that has changed is that his incompetent, malicious, and criminal handling of the country, has increased the danger to everybody in the United States AND the world. Would 120,000 people have died from COVID-19 if President Obama was in office? I would bet my house NO. We would have been on the ground in China, directing resources to keep it there and contain it. Anything that came over to the US would have been quarantined and traced and our numbers would have been like South Korea or Taiwan's. The economy wouldn't have crashed, and we would be functioning in a more normal manner than we are now.
Back to the topic, Trump is not JUST becoming self destructive. He has ALWAYS been that way. He is not trying to lose the election. He is just incapable of regulating his emotions and he lacks the ability to behave in a pro-social manner. There is no planning, there is only reaction. He is only dangerous because he has been given real power and not just his impotent bluster when he grifted his way into the White House.