We can’t really know, because — an interesting fact in its own right — Gallup didn’t poll Americans about their perceptions of King in 1967 and 1968. But King was never a popular figure among Americans, and especially, we can safely presume, white Americans. By 1966 he was extremely unpopular with the public as a whole, and outright despised by nearly half the population (in other words his popularity looked a lot like Trump’s does today):
August 1963 (March on Washington, I Have a Dream speech)
Favorable 41 Unfavorable 37 Highly Favorable 16 Highly Unfavorable 25
Favorable 44 Unfavorable 38 Highly favorable 16 Highly Unfavorable 25
Favorable 45 Unfavorable 46 Highly favorable 20 Highly unfavorable 31
Favorable 33 Unfavorable 63 Highly favorable 12 (!) Highly unfavorable 44
What happened in the three years between the March on Washington and the summer of 1966? Dave Weigel:
In 1965 and 1966, King started working on housing in northern states, starting in Chicago. The 1966 Gallup poll here was taken around the time of the disastrous Marquette Park march, which King credited for the ugliest crowd of counter-protesters he’d ever seen. (We can read some hyperbole into that if we like.) He was starting in on his anti-war activism. He had moved on from the causes of Southern integration and voting rights to the far more volcanic issues of housing and red-lining and economic redistribution — he became, fully, a man of the left.
Weigel could have also mentioned the effect of the Watts riots the previous summer, which were captured as they were happening by the relatively new medium of local TV news, and then offered up to a horrified [overwhelmingly white] national audience (Rick Perlstein documents this in his essential book Nixonland).
Safely dead, Martin Luther King has become, as Erik has noted, a guy who gave one speech that was about how nobody should ever “see” race, or something.
Favorable 94 Unfavorable 4 Highly favorable 69 Highly Unfavorable 1