Mr Moore justified his scepticism of Mr Trump's diagnosis by citing the president's many lies and incorrect statements.
"There is one absolute truth about Trump: He is a consistent, absolute, unrelenting, fearless, and professional liar. A serial liar. A factually proven liar. How many lies now has the Washington Post proven in these four years? 25,000? A lie at least twice during every waking hour? Think of all the bad people you’ve known in your life. Even the worst ones you couldn’t say that about.," he wrote.
Mr Moore then asked "so why on earth would we believe him today? Has he earned your trust now?"
He pondered why Mr Trump would "all of a sudden just start telling the truth."
"Why would you believe him now?" he asked. "...Trump has a history of lying about his health. His longtime New York doctor, Dr Bornstein, admitted a few years ago that Trump dictated his perfect ‘doctor’s letter’ during the 2016 campaign. Then there was the White House doctor who said Trump could live “200 years!” What about his lying about that emergency trip to Walter Reed “to complete his physical?”
Mr Moore said that Mr Trump may have the virus, but said the president lying about the virus had to be considered.
He went on to speculate as to why Mr Trump would fake having the virus after spending months downplaying its danger and publicly undermining guidelines meant to mitigate its spread.
Mr Moore believes the president is responding to polling data that suggests he is falling behind his campaign rival in the 2020 US election, Democrat Joe Biden. Under Mr Moore's theory, Mr Trump hopes to change the media narrative and garner sympathy amoung the public by pretending to have the virus.
"Democrats, liberals, the media and others have always been wrong to simply treat him as a buffoon and a dummy and a jackass. Yes, he is all those things. But he’s also canny. He’s clever. He outfoxed Comey. He outfoxed Mueller. He outfoxed 20 Republicans in the GOP primary and then did the same to the Democrats, winning the White House despite receiving fewer votes than his opponent," Mr Moore wrote. "He’s an evil genius and I raise the possibility of him lying about having Covid-19 to prepare us and counteract his game. He knows being sick tends to gain one sympathy. He’s not above weaponizing this."
He then went on to claim that Mr Trump may use his potentially phony diagnosis to attempt to delay or otherwise postpone the election. Mr Moore notes that the US Constitution does not grant the president the power to move the election, but says Mr Trump and his administration will simply ignore it.
"He and his thug Attorney General Barr have no shame and will stop at nothing to stay in power. He may even use this as an excuse for losing," Mr Moore wrote.
He concluded by admitting that Mr Trump "probably does" have Covid-19, and calling on voters to stick to their plans to vote and to be sceptical about what they read and hear. He then offered his well-wishes - mixed with a sizeable amount of indignation - to Mr Trump.
"Finally, on a personal note: Stay alive Mr. President. Your exit from public life must happen in the right and decent way. You have many years to live. You have a child to raise. Grandchildren who need you. A base that loves you," Mr Moore wrote. "And the families of nearly the quarter-million dead who might be alive today had you done your job, had you cared, had you not played politics with people's lives. Over 200,000 lost souls — and YOU KNEW! You told Woodward in February it was a plague. 200,000 dead because of decisions you made, because you denigrated science and ignored the doctors."
Just before Mr Trump and First Lady Melania Trump announced their diagnosis, White House staffer Hope Hicks tested positive for Covid-19. Since their diagnosis, several other individuals in Mr Trump's orbit over the past few days have tested positive as well, including the president of Notre Dame, a White House staffer, and two reporters who work in the White House.