He's clearly not the same man he once was, but then, he is 80. Even Dianne Feinstein showed mental decline in her 80s, and all she's done for 40 years is sit in a comfy chair and bark orders at people!
The Biden Presidency all but admits this - look at how quickly they're trying to get stuff done - infrastructure, green energy, jobs, protections we take for granted in the UK - all at once, because it's a 4 year tenure, not an 8 year one. Which so far has worked - Biden's managed to get more of his plans passed through the Senate than any democrat since LBJ? FDR? A long time anyhow.
But...the problem is, that Democrats seemed to buy into the Hilary Clinton or bust idea for so long, they never built up any potential challengers. So she sunk, and they're a bit like Labour in 2010 - where's the contenders? (No, Bernie Sanders is 81, he's not the answer, sorry fans.) This is of course why Biden came out of retirement in 2020, as the only popular name who could beat Trump. He'll retire into the sunset in January 2025 and tbf he's earned it.
i don't know who they've got to replace him, though.