The Dutch government blocked the visit of a Turkish official so the Turkish president called them "fascists." Protests at the Turkish embassy were put down by Dutch riot police. These countries are both in NATO.
The Turkish official was to visit to campaign for a Turkish referendum that would expand the powers of Turkey's president, Recep Erdogan. It's a continent-wide campaign because of all the Turks living in other European countries.
Why it matters: Dutch parliamentary elections are March 15. The ruling party is threatened by a far-right, populist party that opposes immigration and the spread of Islamic culture in the Netherlands. According to the New York Times, the far right-party was quick to condemn the Turkish visit and was followed by government action and approval other Dutch politicians. Similar things have happened in Germany and Switzerland.