Slovak Prime Minister Robert Fico vowed on Sunday to block Ukraine from joining NATO for as long as he is head of the country’s government. NATO’s leadership wants Ukraine to join the military alliance after its war with Russia ends in order to deter further aggression from Moscow, but Fico’s declaration highlights the political difficulties that are likely to arise in pursuing that aim. “As long as I am head of the Slovak government, I will direct the MPs that are under my control as chairman of the [ruling Smer] party never to agree to Ukraine’s joining NATO,” he said…