In this Jan. 29, 2008 file photo, Sen. Claire McCaskill, D-Mo., right, listens to Democratic presidential hopeful Sen. Barack Obama, D-Ill.,talk with reporters during a flight from Washington to Wichita, Kan. The plainspoken former prosecutor and state auditor has been all over TV news and political talk shows as a top surrogate for Obama's campaign. (AP Photo/Charles Rex Arbogast, File)

In this Jan. 29, 2008 file photo, Sen. Claire McCaskill, D-Mo., right, listens to Democratic presidential hopeful Sen. Barack Obama, D-Ill.,talk with reporters during a flight from Washington to Wichita, Kan. The plainspoken former prosecutor and state auditor has been all over TV news and political talk shows as a top surrogate for Obama's campaign. (AP Photo/Charles Rex Arbogast, File)

This Jan. 29, 2008, file photo shows Sen. Claire McCaskill, left, D-Mo., watching as Democratic presidential hopeful Sen. Barack Obama, D-Ill., speaks to supporters in Kansas City, Mo. McCaskill, a superdelegate, said older women particularly feel that Sen. Hillary Rodham Clinton is their only hope of seeing a woman occupy the Oval Office, and that one refused to talk with her during a Democratic fund raiser in early April. One Obama's next tasks is to heal the rift with female voters. (AP Photo/Dick Whipple, File)

Sen. Claire McCaskill, D-Mo., left, asks a question during a hearing on Capitol Hill in Washington in this Dec. 4, 2007 file photo. Sen. Thomas Carper, D-Del. is at right. McCaskill, co-author of legislation creating a special commission to examine wartime contracting, said poor-performing contractors are more likely to get bonuses than to be penalized. "It has just been a mess," McCaskill, a former state auditor, said in an interview with The Associated Press. "It's bad enough how much this war is costing. But it's heartbreaking the amount of money that has just gone up in smoke." (AP Photos/Susan Walsh, File)

Flanked by Missouri State Senator Claire McCaskill, left, and Kansas Governor Kathleen Sebelius, right, Democratic presidential hopeful Sen. Barack Obama, D-Ill., speaks to supporters at a campaign stop Tuesday, Jan. 29, 2008 in Kansas City, Mo. (AP Photo/Dick Whipple)

Senate Homeland Security and Governmental Affairs subcommittee member Sen. Claire McCaskill, D-Mo., left, asks a question of credit card executives during the subcommittee's hearing on Capitol Hill in Washington, Tuesday, Dec. 4, 2007 on credit card practices and interest rate increases. Sen. Thomas Carper, D-Del. is at right. (AP Photos/Susan Walsh)