(CNN) - A few of the "could have been" running mates for presumptive GOP nominee Mitt Romney were added to the list of speakers for this month's Republican National Convention Thursday, including Louisiana Gov. Bobby Jindal, Sen. Rob Portman of Ohio, Sen. Kelly Ayotte of New Hampshire and Virginia Gov. Bob McDonnell.
All four names were considered potential vice presidential picks for Romney, who on Saturday announced House Budget Committee Chairman Paul Ryan of Wisconsin as his running mate. Jindal campaigns for Romney Thursday in Virginia.
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Also added to the convention slate: Rep. Connie Mack, who won Tuesday's U.S. Senate primary in Florida and will challenge Democratic Sen. Bill Nelson in November; and Artur Davis, the former Democratic congressman from Alabama who said in May he was backing Romney.
In 2008, Davis spoke at the Democratic National Convention in Denver, and seconded President Barack Obama's official nomination. This week he hit the campaign trail for Obama's Republican challenger in Virginia.
"This exciting group of headliners includes two successful governors, two outstanding senators, the next senator from our convention state, and a former Co-Chairman of the 2008 Obama campaign," Republican National Committee Chairman Reince Priebus wrote in a statement. "The perspectives and ideas they bring to the convention stage will show all Americans that Romney and Ryan are the ticket to a better future. Former Congressman Davis especially will give voice to the frustration and disappointment felt among those who supported President Obama in 2008 and are now hungry for a new direction."
Earlier this week Republicans announced New Jersey Gov. Chris Christie as the keynote speaker at their convention, and said Florida Sen. Marco Rubio would introduce Romney and officially enter his name into nomination. Other Republicans scheduled to speak include former Secretary of State Condoleezza Rice, Arizona Sen. John McCain and former Florida Gov. Jeb Bush.
The 2012 Republican National Convention begins Monday, August 27 in Tampa. Democrats hold their convention the next week in Charlotte.
CNN's Kevin Liptak contributed to this report.
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