June 10 (Reuters) - Former President Donald Trump used the first public appearance since his federal indictment to ratchet up attacks on the Justice Department, accusing prosecutors, without evidence, of a politically motivated campaign to keep him from the White House. In a wide-ranging and at times dark and conspiratorial speech, Trump portrayed his campaign to return to the White House as part of an "epic struggle" to defeat the "sinister forces" that he said were a bigger threat to the country than foreign adversaries like Russia, North Korea and Iran. Trump told the audience in Georgia that the "joke of an indictment" would further bolster his support within the party, similar to how charges in New York in March over hush-money payments to a porn star elevated his ranking in primary polls