I think it will be awhile before we see any "landslide" victories in elections again. Gone are the days of Ronald Reagan winning 48-states or George HW Bush capturing 40-states. And it's not so much the actions of the two political parties in "rallying support" or "identifying key demographics" in their campaign efforts. The real cause can be found in numbers put together by the Wall Street Journal a few weeks ago--showing that 49.1% of US households are getting some kind of government benefits.
That is up from just 30% of households being on the dole back in 1983--and up from 44.4% at the start of President Obama's administration. There are certain demographic factors that contribute to that increase. We are living longer--so people are staying on Social Security and Medicare longer. But there have certainly been political moves to push that number higher as well--such as expansion of Medicaid programs, the food stamps program and extension of unemployment benefits.
And that increase has been a big factor in the resurgence of the Democratic Party since the 1980's. Scare tactics like "Republicans want to cut Social Security and Medicare" or "Republicans want to take away your health care benefits" don't work if a large population isn't receiving Social Security, Medicare or Medicaid. Dependence breeds political support.
The left is trying to portray this election cycle as a "battle" between the "haves and the have nots". But it's clearly more of a showdown between the "givers and the getters". And once the balance goes to the "getters", the "givers" would face an almost impossible task of ever getting out from under that burden.