The dooming and "defeatist attitude" from some Dems gets kind of tiresome, imho. You would never hear a GOPer say stuff like that, even if their prez was at low 30s approvals. They always act and talk like winners and fighters, and that's what most people like.
Sure, things are not exactly going the way they should because (a) we lack a clear governing majority in congress to get stuff done while the GOP is unwilling to actually govern and (b) Biden is not a particularly charismatic politician, although he has his strengths such as personal engagement with voters and a ton of experience.
Just because Biden has medicore approvals at this point in time doesn't mean he - or any D candidate - is DOA in 2024. The previous presidents back to Clinton, and even some before, looked more vulnerable than they were in the end. The election won't take place for another 2.5 years, which is a lifetime in politics.
While this is true for Clinton this isnt really true for Obama despite how bad the 2010 election ended up being. Even in 2011 while Obama had moments where his approvals dropped below 38% they then would quickly go back up as Obama had a far far more enthusiastic base of support than Biden ever has had.
https://www.realclearpolitics.com/epolls/other/president_obama_job_approval-1044.html