The terrorist attack in New Zealand has focused attention once more on the acute threat posed by rightwing extremists.
Waves of terrorism follow a pattern: a long, unnoticed buildup followed by a massive and spectacular strike that often inflicts significant damage and casualties but focuses minds and eventually resources.
Counterterrorism agencies, driven by public outrage and concerned officials, struggle for a time to gain the upper hand until, with better funding and understanding, they begin to win the battle to keep us safe. The cycle can take many years, even decades.