WASHINGTON — Longtime Michigan Republican U.S. Rep. Fred Upton said Tuesday he will retire from the House at the end of his term after nearly 36 years in office, ending speculation about his political future that had swirled for months. The St. Joseph lawmaker made the announcement on the House floor, bringing to a close months of indecision by Upton, who, at 68, is Michigan’s most senior lawmaker in Congress — a moderate conservative first elected to the U.S. House in 1986. “Even the best stories has a last chapter: This is it for me,” Upton said. In an email sent to supporters and friends Tu…