Based on the Preface, Introduction and chapters 1-4 of Ian Haney López's Dog Whistle Politics: How Coded Racial Appeals Have Reinvented Racism and Wrecked the Middle Class What is soft-porn racism?

The answer to this question can be found in Chapter One, or "The GOP's Rise as 'the White Man's Party'." This chapter describes the ascent of George Wallace, the "redneck poltergeist" who began serving as the governor of Alabama in January of 1963 under the auspice of protecting segregation.
After losing the 1958 election because of relatively "soft" stance on race, Wallace ran again in 1962; this time, he veered far right on the issue of race, even going as far as to court the support of the Ku Klux Klan. Wallace quickly became adept at exploiting White hatred of Black individuals using non-racial language. He used the concept of "states' rights" as an abstraction to represent white supremacy; this technique of raising fear and hatred without mentioning race (and, in fact, denying that one is racist) became known as "soft porn racism."
Wallace realized that the language of racism was increasingly rejected, and, thus, he created a new vocabulary to articulate white supremacy without "overtly transgressing prescribed social limits." López articulates this by explaining:

Hardcore racism showed white supremacy in disquieting detail. In contrast, the new soft porn racism hid any direct references to race, even as it continued to trade on racial stimulation.