Washington (CNN)Donald Trump's travel ban on seven Muslim-majority nations marks an early defining moment for his presidency and an inflection point in America's posture toward Islam and the outside world that could resonate in history. The move, which also temporarily bars refugees from entering the US, ushers in the first clash between Trump's populist and proudly politically incorrect leadership style and what his critics see as bedrock values that define the nation. It also represents a pronounced shift in US counter-terrorism tactics and a sharp turn in the debate underpinning national security policy since the 9/11 attacks -- how to best keep Americans safe and battle extremism at home...
