Donald Trump pleaded not guilty Tuesday to dozens of criminal counts of mishandling some of the US government's most sensitive secrets and scheming to prevent their return, in a historic first court appearance as a federal defendant. The former president -- and the favorite to fight next year's election for the Republicans -- gave himself up to US Marshals in Miami for a hearing that set up the unprecedented scenario of a White House race litigated from the courtroom as well as at the ballot box. On the eve of his 77th birthday, Trump appeared before a magistrate judge to be formally presented with 37 counts under seven charges brought by a special counsel probe that opened after an FBI raid of his Florida mansion 10 months ago.