I will go on record in disagreement.
The country is too ideologically divided now. We will never see "a Republican landslide" again, and any elections in which a Republican wins the presidency will be by relatively close margins or else by the Electoral College only.
Absolutely fearless prediction:
There will never be a victory like the one Reagan had in 1984 again.
Those days are over for America.
At least for America as it exists NOW (i.e., in our "pre-2nd-civil-conflict" stage).
Perhaps AFTER that "conflict" (whatever form it's going to take, as yet this is unknown), and AFTER "the Reconstruction" that follows, landslide victories in presidential elections may again occur.
But for right now, them days is over.