When a group of European officials arrived in Kyiv to mark Ukraine’s Independence Day last month, they got some worrying news. The European Union, a key backer, had earlier this year finalized a loan of more than $100 billion for the country. But Ukraine now faced an unexpectedly large defense budget shortfall, President Volodymyr Zelensky told allies. To get through the year, he would need $27 billion more. Europeans understand Ukraine is in a fight for its existence but did not expect such a large budget shortfall, according to four European diplomats who, like others quoted in this piece, spoke...