European Union leaders launched a day of emergency talks Thursday in a bid to beef up their own security and ensure that Ukraine will still be properly protected. Friedrich Merz, the likely next chancellor of Germany, and summit chairman Antonio Costa discussed over breakfast in Brussels ways to fortify Europe’s defenses on a short deadline. Merz pushed plans this week to loosen the nation’s rules on running up debt to allow for higher defense spending. Meanwhile, the 27-nation bloc was waking up to news that French President Emmanuel Macron would confer with EU leaders about the possibility of using France’s nuclear deterrent to protect the continent from Russian threats. It all underscored the sea change that has taken place in the two months since Trump took office and immediately started upending the cornerstones of cooperation between the United States and Europe that had been the bedrock of Western security since World War II.