I think it might backfire. They're setting expectations so low with the constant "Joe has dementia and his brain is a scrambled egg...He can't even talk!" such that as long as Biden shows up to the debate and survives for two hours without ting his pants or collapsing on stage the media narrative will be "Joe Biden fights back and shows he doesn't have dementia!"
The Dems made the same mistake in 2016. They talked nonstop about how "unpresidential!" Trump is, then after the 3rd debate (where Trump intentionally toned it down), the story that dominated headlines was "Trump shows he can be presidential!"
The 1st debate is a trap for Trump. Reagan, GHWB, GWB and Obama all didn't take their first reelection debate seriously and had to make up ground in the 2nd and 3rd debates. In the Axios interview Trump looked totally unprepared for a scenario where someone is going to push back and challenge what he says, he's gonna need a lot of prep to get back into 2015 Teflon Don mode.