CARACAS, Venezuela —President Nicolás Maduro’s call to hold a “mega-election” that could obliterate the opposition-dominated legislature was met Thursday with a storm of protest from politicians facing an ever-bleaker future. In a news conference Wednesday, Maduro proposed moving up legislative elections originally scheduled for 2020. They would be held alongside a snap presidential election scheduled for April 22. The socialist president made the move after the opposition refused to participate in the presidential election because of what it called fraudulent conditions. “The government believes with this announcement and its thirst for power that it can change the reality in the country,” said Stalin González, an opposition legislator, in a tweet.