...1976 versus 1992 and 1996. Carter barely got elected in 1976 with the aid of states that would never vote for a Democratic nominee for President for at least forty years. Carter's failed Presidency (the Reagan landslide of 1980 makes that an inevitable judgment) led to three Republican landslides before any Democrat could win again. Oddly, Bill Clinton seems similar in ideology and culture to Jimmy Carter, so it is not a matter of finding a Democratic nominee from the West Coast, Midwest (Mondale from Minnesota in 1984 was a disaster), or New England (Dukakis from Massachusets in 1988 was a failure).
These three Democratic wins involve the "New South" -- the South between the 1964 Civil Rights Act and the completion of the success of the Southern Strategy.
It's not a perfect match (there was a third-party nominee getting lots of votes), but I am showing the one Carter win to the two (Bill) Clinton wins:
Ford, Bush, Dole -- blue
Carter, Clinton once -- pale blue
Carter, Clinton never -- yellow
Ford -- but Clinton twice -- white
Carter, Clinton twice -- red
1992 is about as clearly a Realignment election as any in the lifetimes of any reader of these forums unless one is very old. Few saw 1992 coming, and the 1992 election looked very different from that of 1976. Clinton won a raft of states -- by the 2012-2016 count 162 electoral votes (in white) -- that Carter lost in 1976. Clinton never won any of the 79 electoral votes from states that except for North Carolina voted for Carter but no other Democrat (NC in 2008 for Obama, and then barely) for President since then.
States in white other than Nevada and (once-barely) New Hampshire and New Mexico have never since voted for any Republican for President beginning in 1992.
There have been near-landslide elections for President since 1988: 1992, 1996, and 2008. 2000 and 2004 were close, and it is hard to characterize 2012 (it is close to the median for the winner in Presidential elections since 1900, but it is the only Presidential election really close to the median in electoral votes).
So why do realignments follow a succession of landslide losses? The winning coalition typically end up with constituencies with diametrically-opposite interests and values on key issues. The winners may take for granted voters that the winners think by nature 'theirs', that is one way to have dissatisfied voters that the Other Side can pick off. Thus the Reagan wins depended upon putting together relatively-liberal "Rockefeller Republicans" and Southern fundamentalists who had little in common.