Mr Giuliani, 76, the president’s personal lawyer, has been leading the legal battle to overturn the results of the election through the courts.
Earlier Sunday, Giuliani appeared on Fox News’ Sunday Morning Futures where he updated host Maria Bartiromo on the efforts to have state legislatures toss election results and appoint a new set of electors.
Mr Trump announced the news on Twitter, saying: “@RudyGiuliani, by far the greatest mayor in the history of NYC, and who has been working tirelessly exposing the most corrupt election (by far!) in the history of the USA, has tested positive for the China Virus. Get better soon Rudy, we will carry on!!!”
Yet, despite the president’s reassurances, his diagnosis certainly throws that process into disarray. The two people previously leading the Trump legal efforts, David Bossie and Corey Lewandowski, both tested positive for Covid and had to step back from the frontline.
Mr Giuliani has spent the past few weeks travelling around the country, attending hearings with crowds of people, indoors and maskless, in multiple states. They will now have to go in to quarantine.
On Monday he was in Phoenix, Arizona; on Wednesday in Michigan; and on Thursday in Georgia, holding hearings inside hotels.
The previous week, he was in Pennsylvania, on 25 November, for a hearing where almost no one was wearing a face mask inside the Gettysburg hotel. Two of the Republican senators at the hearing have since tested positive for Covid.
They include Doug Mastriano, the fervently pro-Trump senator who called the hearing with Mr Giuliani, and was informed of his positive test while at a West Wing meeting with Mr Trump hours after the hearing.
At one of the hearings Mr Giuliani, who like his boss is almost never seen wearing a face mask, asked a woman testifying to remove hers, because he said he couldn’t hear her.
It was unclear whether he had so far attended any of Mr Trump’s 20 White House Christmas parties, where photos have shown tightly packed, maskless revellers crammed into the rooms.
The former mayor of New York’s son Andrew, 34, who works in the White House and is a frequent golf partner of the president, tested positive earlier this month.
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