Romney's VP choice: Rep. Paul Ryan, R-Wis.

Ryan,_Walker,_Romney.JPG — Joe Raedle/Getty Images

Republican National Committee Chairman Reince Priebus, Rep. Paul Ryan, R-Wis., Republican presidential candidate Mitt Romney and Gov. Scott Walker, R-Wis., wave together during a campaign event at Monterey Mills on June 18, 2012 in Janesville, Wisconsin.

Rep. Paul Ryan, R-Wis., looks on as Republican presidential candidate Mitt Romney greets people during a campaign event at Monterey Mills on June 18, 2012 in Janesville, Wis.

House Budget Committee Chairman Paul Ryan, R-Wis., questions Congressional Budget Office Director Douglas Elmendorf during a hearing on Capitol Hill June 6, 2012 in Washington, D.C.

Republican presidential candidate Mitt Romney greets Rep. Paul Ryan, R-Wis., before speaking to supporters during his primary night gathering at The Grain Exchange on April 3, 2012 in Milwaukee.

Republican presidential candidate Mitt Romney and Rep. Paul Ryan, R-Wis., greet supporters as they hand out sandwiches to supporters at Cousins Subs on April 3, 2012 in Waukesha, Wis.

Republican presidential candidate Mitt Romney speaks during a town hall style meeting as Rep. Paul Ryan, R-Wis., looks on at Wisconsin Building Supply on April 2, 2012 in Green Bay, Wis.

House Budget Chairman Rep. Paul Ryan, R-Wis., is introduced before speaking about "America's Enduring Promise," and the federal budget, in a speech at Georgetown University, April 26, 2012 in Washington, D.C. During his speech, Ryan said that his proposed budget confronts the nation's growing $15 trillion debt before it impacts future generations of Americans.

House Budget Chairman Rep. Paul Ryan, R-Wis., is introduced before speaking at Georgetown University, April 26, 2012 in Washington, D.C.

House Budget Committee Chairman Rep. Paul Ryan, R-Wis., speaks during a news conference after a House Republican Conference meeting July 18, 2012 at the Capitol Hill Club in Washington, D.C.

Republican presidential candidate Mitt Romney and Rep. Paul Ryan, R-Wis., hold bags of food at a Culver's restaurant on April 1, 2012 in Johnson Creek, Wis.

House Budget Committee Chairman Rep. Paul Ryan, R-Wis., speaks on Capitol Hill in Washington, Tuesday, July 10, 2012.

Speaker of the House Rep. John Boehner, R-Ohio, speaks as Rep. Paul Ryan, R-Wis., House Majority Leader Rep. Eric Cantor, R-Va., and Rep. Martha Roby, R-Ala., listen during a news conference after a House Republican Conference meeting July 18, 2012 at the Capitol Hill Club in Washington, D.C.

In a Dec. 7, 2011 file photo, House Budget Committee Chairman Rep. Paul Ryan, R-Wis., second from right, accompanied by fellow committee members, gestures during a news conference on Capitol Hill in Washington . From left are, Rep. Diane Black, R-Tenn., Rep. Tom Price, R-Ga., Ryan, and Rep. Jason Chaffetz, R-Utah.

Mitt Romney and Paul Ryan — AP Photo/M. Spencer Green

House Budget Committee Chairman Rep. Paul Ryan, R-Wis., introduces Republican presidential candidate Mitt Romney before Romney spoke at the Grain Exchange in Milwaukee, Tuesday, April 3, 2012.

Republican presidential candidate Mitt Romney shares a laugh with Rep. Paul Ryan, R-Wis., Chairman of the House Budget Committee and Sen. Ron Johnson, R-Wis., left, during a campaign stop at a pancake breakfast in Milwaukee, Sunday, April 1, 2012.

Rep. Paul Ryan, R-Wis., Chairman of the House Budget Committee, left, and Republican presidential candidate Mitt Romney, right, wave to the audience as Romney takes the stage during a campaign stop on the campus of Lawrence University, in Appleton, Wis., Friday, March 30, 2012.

Rep. Paul Ryan, R-Wis., on CBS News "Face the Nation", Sunday, March 25, 2012.

CBS News' Bob Schieffer interviews House Budget Committee Chairman Paul Ryan, R-Wis., for the January 25, 2012 edition of "Face to Face"

House Budget Committee Chairman Paul Ryan, R-Wis., works with Republican members of the committee on Capitol Hill in Washington, Tuesday, April 5, 2011. At right is committee member Rep. Tom McClintock, R-Calif.

House Republican leaders hold a news conference on Capitol Hill — AP Photo/Carolyn Kaster

From left, House Ways and Means Committee Chairman Rep. Dave Camp, R-Mich., Rep. Diane Black, R-Tenn., House Budget Committee Chairman, Rep. Paul Ryan, R-Wis., Republican Conference Chairman Rep. Jeb Hensarling, R-Texas, and House Majority Leader Eric Cantor of Va., participate in a news conference on Capitol Hill in Washington, April 13, 2011.