After all these years, we’ve come to realize that economists – that is, real economists – don’t believe in so-called supply-side economics at all.
From today’s The New Republic, Dismal Scientists vs. Credulous Public:
“Permanently raising the federal tax rate by one percentage point for those in the top income tax bracket would increase federal tax revenue over the next 10 years.”
This is a bit like saying if you jump into a swimming pool you’ll get wet. When researchers at the University of Chicago’s Booth School of Business and Northwestern’s Kellogg School of Management presented this statement to a “panel of distinguished economists,” 100 percent of them agreed with it. But when the researchers presented this statement to the general public only 66 percent of respondents agreed with it. Only fifty percent of Republicans agreed with it, compared to 80 percent of Democrats. “This difference exists in spite of the fact that this statement is factual, not political,” the researchers observed. “Indeed, all economists, regardless of their political orientation, agree with it.”
Why does a substantial percentage of the public continue to believe in something experts don’t? Because, for several high-profile political candidates, expressed faith in the supply-side fairies is a foundational element of their campaign communication. Repeat something often enough and passionately enough, this seems to suggest, and you can get a lot of people to believe in almost anything.
Speaking Plainly 
You nailed it. And the sad thing is that today’s Republican base lives in an upside down world where macroeconomic experts are wrong about the effects of spending and taxes, climatologists are wrong about the climate, and the 2008 crash was caused not by peddlers of frudulent, worthless, mortgage-backed securities but by the Fed/Barney Frank/FreddieMac. But Fox and its kind work so hard to make people comfortable believing these falsehoods. I wonder if the candidates almost have to toe these lines?
No almost about it. Ceaselessly repeating that set of falsehoods is the price of playing the game.