WASHINGTON — Former President Bill Clinton will have a marquee role in this summer's Democratic National Convention, where he will make a forceful case for President Barack Obama's re-election and his economic vision for the country, several Obama campaign and Democratic party officials said Sunday.The move gives the Obama campaign an opportunity to take advantage of the former president's immense popularity and remind voters that a Democrat was in the White House the last time the American economy was thriving.Read More... More on Barack Obama