President Obama arrived in Portland just before 4 p.m. Thursday for an appearance to boost Democratic U.S. Rep. Mike Michaud’s campaign for governor. Obama will headline a rally at the Portland Expo, featuring Michaud and other Democratic candidates, later Thursday. The president arrived on Air Force One, which taxied into position in front of Maine Aviation Corp at the Portland International Jetport at 3:55 p.m.. Obama stepped off the plane a minute later and was greeted by Michaud, the six-term congressman who is running against incumbent Republican Gov.