Arianna Huffington and Michael R. Bloomberg: In recent years, as Washington has sunk further into a swamp of dysfunction, local leaders are rising to meet many of the toughest challenges facing the country — from economic growth and environmental protection to public safety and poverty. Cities have become the new laboratories of democracy, and there are promising policy experiments happening all across the country. Solutions to many of our most pressing challenges will need to be pioneered in cities — and, based on what is already happening, we have great faith and optimism that they will be. Today, on behalf of The Huffington Post and Bloomberg Philanthropies, we are excited to launch a new platform that celebrates the boldness and creativity of mayors and cities across the country. Here you can weigh in and help choose the Mayors Challenge Fan Favorite — the civic innovation that Americans most want to see succeed.