The letter was intercepted during routine screening before it could reach the White House.
The US president visited his brother at a New York City hospital on Friday after White House officials said he had become seriously ill.
The US President described the latest figures as 'very encouraging', 24 hours after the White House coronavirus response coordinator warned the US was entering a 'new phase' of the pandemic.
Could Trump be removed from office? Euronews takes a look at what we know so far and what's next.
Andrew Peek, who has been advising the president on Europe and Russia issues, has been placed on administrative leave pending an investigation.
"Also began phase one of my yearly physical," Trump tweeted early Sunday. "Everything very good (great!). Will complete next year."
The move comes hours after the administration blocked the testimony of U.S. ambassador to the EU Gordon Sondland.
While many in the Trump White House are battle-tested from the Mueller investigation, this time is starting to feel different, aides and advisers said.
A tree planted by Donald Trump and his French counterpart Emmanuel Macron as a symbol of their countries’ ties has died, according to multiple media reports in France.