So now the left doesn't know what Western Civilization is?

Prominent elements of the left think it's about skin color, lol. No, more like liberty, citizenship, rule of law rather than men, egalitarianism, science, constitutionalism, productivity, free and open debate, an unmatched intellectual and artistic tradition, and yes Christianity, though with freedom of religion for all. Combinations of the above factors have typically resulted in superior organizational skills and innovation that, along with troops having a personal stake in the society they're fighting for, have usually led to conventional military dominance versus non-Western armies for the past 2,500 years.

These are deeply held cultural ideals accumulated over the millennia that aren't based on skin color. Western Civilization began in classical Greece and later spread to the rest of Europe, influencing most of the planet to varying degrees in the modern era. The Greeks invented citizenship as we understand the concept, meaning that instead of being merely subjects of a ruler they were stakeholders in a state to whom rulers were accountable. Kings weren't worshiped as gods and had limits to their powers, while some Greek city states ditched monarchy altogether to form various kinds of republics, most famously Athenian democracy. Policies were debated openly by voters and government officials, giving rise to the art of rhetoric. The Greeks also developed formal mathematics (complete with proofs), formal logic, and fields like philosophy, history, and medical study. Rome rose under heavy Greek influence and spread these values around the known world, along with Western architecture, engineering, and the functional alphabet we still use today.

Christianity infused the West with a moral/spiritual dimension it had previously lacked. Christianizing the Germanic barbarians who had taken down a Roman Empire that had rotted from within was the conduit through which they were gradually Westernized, laying the foundation for modern Europe. Some German cultural traditions were compatible with and even enriched Western principles, like a greater emphasis on individual liberty, property rights, and jury trials. Others, like human sacrifice and casual infanticide, were dispensed with by Christian preaching as gladiator games and similar classical pagan practices had been. The Christian West became the only civilization to independently outlaw slavery, an institution pervasive throughout the world for most of human history. It did so twice, first in Medieval Western Europe because it became seen as wrong to hold fellow Christians in bondage, and later with black slavery, a common African practice imported to the West in the early modern era by seagoing traders doing business with local tribes that was abolished with Christian activists leading the way. Afterwards Western powers, first Britain and then the US, used their strength to pressure Muslims and others to end slavery in the 20th Century. Our notion of universal equality is an outgrowth of the Christian belief that God loves and values every person, and it would not otherwise exist.

The Christian West also invented true science around 400 years ago, and for much of the past 1,000 years saw art and music flourish at a higher level than at any time in human history, from Michelangelo to Leonardo Da Vinci to Mozart to Beethoven.

Christianity, married to Western philosophy, provided a basis for natural rights political theory in the early modern era. Liberty and equality were now seen as universal rights given by God rather than preferences of the moment for a chosen few and dependent on the whims of the strongest armed force as even the Athenians had viewed them. The USA espoused these principles in its founding documents and revolutionized global politics. Religious freedom grew from them and because the twin developments of mass printing and mass literacy let people read for themselves that in the New Testament Christianity is supposed to be voluntary.

The rise of free market economics in recent centuries has created more wealth and lifted more people out of absolute poverty than anything else in history. Marxism is also an outgrowth of Western Civilization, though arguably representing its dark side, and one rejecting several core Western values even as it's proved seductive enough to be embraced by much of the non-Western world. In the Cold War the freer West proved stronger than the socialist version.

None of this has anything to do with skin color. Westerners tend to be "white" simply because Western Civilization happened to begin in Europe. Trump's comments about defending Western Civilization from terrorists were spot on. It's not even about religion per se, since some Muslims are thoroughly Westernized, especially in America. But Islamist ideology, militant Islamic theocracy that manifests itself in things like terrorism, honor killings, and strict sharia law, are antithetical to religious freedom and other Western values.