U.S. President Donald Trump’s new national security strategy appears to blow up some of the key principles behind 80 years of European collective defence, challenging the foundation of the continent’s relationship with the country. But on whether the White House will — or even can — follow through on many of its more radical or transformative demands, many European capitals will likely need more convincing. In a blistering attack, Trump’s new policy portrays Europe’s governments as weak and ineffective. Migration has destroyed the continent’s self-confidence, it claims, accusing the European Union of contributing to a loss of national sovereignty, weakened...