I don’t think he’ll back out of the debate. I’m sure Kristin Welker has been given explicit instructions that Trump cannot, under any circumstances, get any questions to Biden about the laptop. They’ve already released the topics for debate...the family, climate change, the virus and anything that goes after Trump.
I don't think Trump can get a fair shake in the debate. I think the Trump campaign should give a lot of consideration to pulling out of the debate Thursday morning after Joe has been off the grid all week. Plus, the news cycle will probably be in Trump's favor this week.
It is a DEBATE. She cannot control all of what Trump says.