1. First, he is heavily attached to the reparations chatter. Once drawn into any debate and this comes up....he will have to explain how this is paid for, and the bulk of working-class Democrats won't easily buy into his explanation.
2. 500,000 residents of California left between 2020 and the end of 2022. As Governor and a potential candidate....he has to explain why.
3. Drug problems in SF and LA? He would have to explain how the problem has only grown, not diminished.
4. Covid record for the Governor? It's not anything you'd want to brag over.
5. Not that it's terribly negative.....but Newsom is a male-model type, and not that clever on debates/arguments.
As for comparing to Obama? Well....Obama had no real record while as a Senator....so you couldn't ding him on failures. You can't say that for Newsom and his actions over the state of California.
Counter-advertising with Newsom? It's a nightmare to view the countless interviews with the people who stayed in California, and those who left.