Fox News reporter Chad Pergram has tweeted that the letter sent to Barack Obama and the letter sent to Senator Roger Wicker yesterday - which tested positive for the poison ricin - contained 'similar language' and were 'signed identically'.
Letters sent to Obama & Wicker contain similar language and are signed identically.
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The Democratic presidential candidate may also have shown his cards on his choice of running mate.
The US president also shared a post on Twitter accusing Dr Anthony Fauci of misleading the public over hydroxychloroquine.
Fears over an impending second wave of coronavirus dominates Wednesday’s front pages.