Republican presidential candidate, former Massachusetts Gov. Mitt Romney, addresses an audience during a campaign stop at an oil company in Milwaukee, Monday, April 2, 2012. (AP Photo/Steven Senne)
April 4, 2012 12:04:08 AM PDT
ANNAPOLIS, Md. --
Mitt Romney tightened his grip on the Republican presidential nomination Tuesday night, sweeping primaries in Wisconsin, Maryland and Washington D.C., with time left over to swap charges with President Barack Obama.