MICHAEL MARTINA, HEATHER TIMMONS and ERNEST SCHEYDER AFTER one of the most bruising U.S. presidential campaigns in modern times, supporters of President Donald Trump and his challenger Joe Biden were angry, frustrated and fearful, with the result still days or even weeks away. Trump's declaration of victory in the early hours of Wednesday, with ballot-counting not yet completed, roiled Biden backers, who are afraid that the Republican president might not accept the election result if Biden wins. Meanwhile, many of those in Trump's voter base were echoing his unsubstantiated allegations of electoral fraud. Either Trump or Biden could end up…