It appears that a significant number of our fellow Americans have gone ‘round the bend.
A spate of surveys shows a significant majority of Americans (maybe 60 percent, a couple of polls report) thinks President-elect Joe Biden won the election. (This is akin to “What color is George Washington’s white horse?”) That means 40 percent or so of Americans are utterly deluded. And with a new appreciation for the inexactitude of polling, it’s possible the portion of Americans who accept Biden’s victory is anywhere from 70 percent to only 50. (Republicans could simply be out to annoy pollsters; on the other hand, pollsters have proved themselves ineffective at sampling enough of the MAGA crowd.)
Regardless, the answer to “How many Americans believe in a baseless conspiracy that the election was stolen?” is “Too many.” In all likelihood, millions upon millions of people believe in something as silly as the idea that UFOs are stored at Area 51. (How far is this from “the DNC server is still in Ukraine”?)