Galvanized by the recent terror attacks in France, European Union leaders on Thursday debate a range of ambitious steps to better protect their 28 nations, including exchanging airliner passenger manifests, tightening controls at the border and combating extremism on the Internet. “Europe is facing an unprecedented, diverse and serious terrorist threat,” Gilles de Kerchove, the bloc’s counter-terrorism coordinator, warned EU member governments in a report last month. Latvian Foreign Minister Edgars Rinkevics, whose nation holds the EU’s six-month revolving presidency, said Tuesday the often fractious members had reached broad consensus on what actions to take, and share the “strong will”...