Trump's tweet comes after Rudy Giuliani appeared on Fox & Friends Thursday morning to speculate about the Federal Bureau of Investigation placing a spy in the Trump campaign - which the lawyer said "would be the biggest scandal in the history of this town".
Trump's tweet refers to an article penned by McCarthy and published by National Review on Saturday.
The tweet, which recalls Trump's unsubstantiated claim that Obama "wire tapped" Trump Tower during the 2016 presidential election, followed a freaky post congratulating America on being in the "second year of the greatest Witch Hunt in American History".
"McCarthy said on Saturday that Glenn Simpson, co-founder of Fusion GPS, told the Senate Judiciary Committee in August 2017 that former British intelligence officer, Christopher Steele had said that the Federal Bureau of Investigation had "'human source'" - i.e. a spy" in the Trump campaign. "The only Collusion was that done by Democrats who were unable to win an Election despite the spending of far more money!" Multiple Trump campaign officials have been charged over their connections with Russia, and over a dozen Russian nationals have been indicted over their role in Russia's interference in the American election. Mainstream outlets have also been commemorating the one-year anniversary of Mueller's appointment as special counsel on May 17, 2017. Manafort has pled not guilty.