That is a good question. I just looked it up and the numbers startled me. I had no idea that the numbers were that high. I can't see how this many different services can produce around the same result.
Gallup Poll [a]
June 11-13, 2016 50% Rasmussen Reports [b] April 2629, 2016 50% FOX News [c] April 1113, 2016 49% NBC/The Wall Street Journal [d] April 1014, 2016 49%