2000 for Democrats, especially because it's likely Gore actually won Florida. And Dubya's presidency was such a disaster that it triggered several negative events in the aftermath.
Not sure 1948 and 2020 are actually "close elections". 2020 only in terms of margins in battleground states, but Biden crushed Trump by over seven million votes.
Well 1948 and 2020 did have the tipping point state be decided by less than 1 point so I’d say it’s definitely close and definitely closer than semi close elections like 1976 and 2004.
Though you could say 1960 was worse for republicans since they pretty much spent the next 8 years completely in the wilderness and democrats pretty much got their entire agenda passed while republicans really didn’t from 2001-2009