BAGHDAD — Iraq’s embattled Prime Minister Nouri al-Maliki, in a surprise speech late Sunday, resisted calls for his resignation and accused the country’s new president of violating the constitution, plunging the government into a political crisis at a time it is battling advances by Islamic State militants. On Sunday night, in a nationally televised speech, al-Maliki declared he will file a legal complaint against the new president, Fouad Massoum, for committing “a clear constitutional violation". “This attitude represents a coup on the constitution and the political process in a country that is governed by a democratic and federal system,” al-Maliki...