SEOUL (Reuters) -When South Korea's Constitutional Court rules on President Yoon Suk Yeol's impeachment, expected in coming days, few will be watching more closely - or be watched more closely for possible rabble-rousing - than the country's activist pro-Yoon churches. Outspoken pastors and their flocks have emerged among the conservative president's most vocal supporters, demanding in mass rallies, online videos and lawmakers' speeches that he be restored to office after his impeachment over a martial law declaration in December. Invoking their religious faith and ardent anti-communism, they have doubled down on support for Yoon and cast his impeachment not as the reining in of a rogue leader, but as an existential threat to the fight against North Korea and other enemies.