You know it is going to happen... Unless the Republican party completely disintegrates and splits into factions, but this does not appear to be happening (a man can dream though). So, what do you think?
The longest one-party rule in the 20th century was 20 years (1933-1953), but this spanned only two presidents. The longest one-party rule in the 19th century was 28 years (!), from 1801 to 1829 (the Democratic-Republican Party).