MACON — Democrat Michelle Nunn on Thursday ramped up her attacks on Republican David Perdue in Georgia’s closely watched Senate race, portraying her opponent as an obstructionist who would continue gridlock in Washington. The two met for their first candidate forum, and Nunn quickly set the tone by highlighting her work leading a major volunteer organization founded by former President George H.W. Bush. She also called out Perdue over his opposition to the academic standards known as Common Core, the most recent farm bill and a bipartisan plan for immigration reform.