Well, I won't argue with you that 66% would indeed be a landslide victory. However, how often does that ever happen? For a candidate to receive 66% of the vote is an extreme rarity. I couldn't imagine something like that happening, unless it occurs in a small election such as a Congressional district or a Mayoral race, or something of that nature. I couldn't even imagine a Governor or Senator winning that large of a majority, unless he or she were VERY popular
Actually a >66% majority occurs very often these days in Senate races. This is of course due to popularity of the candidate but also because in some very uncompetitive states the other party often doesnt field a serious candidate.
Off the top of my head I can Indentify John Kerry, Robert Byrd, Jay rockerfeller on the dem side and Jon Kyl (91% I think) Thad Cochan and Jon Warner (GOP) who have crossed 66% and there are many more.
Till the 70's and actually after democrats in the South would be ashamed if they got any less than that (66%)
Governors do it too though not that often. Kenny Guinn (R-Nevada) did it in the last election.
and of course you are right at the congressional and local level 66% is all too common.