Donald Trump rattled off a series of social media posts demanding presidential immunity and threatening his predecessors before heading into the fourth day of his criminal trial Friday. The U.S. Supreme Court will hear arguments next week in Trump’s appeal of his Washington, D.C., election subversion case, in which he claims to have broad immunity as a former president, and he issued what sounded like a threat to prosecute his immediate predecessors and his chief Democratic rival Joe Biden. “If a President does not have Immunity, the Opposing Party, during his/her term in Office, can extort an…