(CNN) - Seeking to rebut what he views as perilous election-year bombast about Muslims, President Barack Obama is at a mosque in Baltimore on Wednesday, his first visit to such a site in the United States."Muslim Americans keep us safe," Obama told the audience, crediting the contributions Muslims have made to communities. "They are our police. They are our fire fighters. They're in (the Department of) Homeland Security." At the Islamic Society of Baltimore, a 47-year-old mosque with thousands of attendees, Obama heralded the contributions of Muslims to American society while issuing a forceful counterpoint to the language favored by...