WASHINGTON, Jan 20 (Reuters) - Hours after retaking the presidency on Monday, Donald Trump issued pardons to around 1,500 of his supporters involved in the assault on the U.S. Capitol four years ago, demonstrating his authority over the government with decisiveness. Following an inaugural day steeped in pageantry, Trump initiated a flurry of executive actions aimed at curbing immigration, rolling back environmental measures, and reversing diversity initiatives concerning race and gender.