When it comes to Washington’s current (and to all appearances permanent) fiscal fracas, the semantic weeds are as high as an elephant’s eye and higher than a donkey’s. In the battles over debt limits, fiscal cliffs, continuing resolutions, and the budget, the clashing sides deploy duelling vocabularies. The Democrats’ revenue enhancements, public investments, and “the one per cent” are the Republicans’ tax hikes, reckless government spending, and “the job creators.” Reading from left to right, the inheritance tax is the estate tax is the death tax. The Dems prevail in a few of these skirmishes, the Reps in a few more. Most are stalemated. But in one of them the conservative side long ago won a decisive victory, a victory at once famous and infamous: “entitlements.”
Hendrik Hertzberg on the Republican rhetorical victory over programs like Social Security and Medicare.
Too bad Google's Ngram viewer doesn't go beyond 2008 now, but even up to then the Google Ngram for entitlements shows a steady rise through the late 1990's, and it's still far above what it was in the 1970's.
Books aren't the ideal or most complete corpus for measuring the use of this term in political discourse, but it does seem to support Hertzberg's thesis.