Tuesday on the NewsHour, a dam breach in Ukraine endangers several cities and prompts evacuations as Russia and Kyiv trade blame. Former New Jersey Gov. Chris Christie launches his bid for the GOP presidential nomination, signaling he plans to take former President Trump head-on. Plus, the mayor of Los Angeles discusses her city's strategy to counteract the alarming increase in homelessness. PBS NewsHour is supported by - https://www.pbs.org/newshour/about/funders