GRAM SLATTERY TIM Scott, the only Black Republican in the U.S. Senate, formally kicked off his 2024 presidential campaign, betting his upbeat message will sell in a party in which many voters are still firmly behind former President Donald Trump. In a speech to supporters in his hometown of North Charleston, South Carolina, Scott, 57, leaned heavily into his personal experience as the impoverished child of a single mother as proof that America remains a nation of opportunity. He emphasized the progress the United States has made on racial issues in recent decades, proclaiming - as he often does -…