Democratic presidential candidate Sen. Barack Obama would be wise to choose U.S. Sen. Sam Nunn as his running mate, and Republican candidate John McCain will find it difficult not to choose Mike Huckabee for the GOP's vice presidential slot, a retired University of Oklahoma professor said Friday.

Speaking at the Cleveland County Democratic Party's weekly Tyner Cornbread and Beans luncheon, Dr. Bill Carmack, former head of OU's Department of Communications, said Nunn and Huckabee present compelling choices for Obama and McCain.

"A vice presidential candidate needs to bring balance to the ticket," Carmack said. "And that balance can be geographical, age, experiences or a combination of those factors. You have to have balance in many areas."

Carmack, himself a former staffer for two U.S. vice presidents and an aide to former U.S. Sen. Fred Harris, said the fall general election will "probably raise ethical questions" about McCain.

"McCain can't run as an outsider," he said. "The man has been in D.C. since God made dirt."

Because McCain could be in danger of losing his outsider status, Carmack said he needs to choose a vice presidential candidate who isn't seen as a Washington insider.

"Sam Brownback has a strong constituency," he said. "And Sarah Palin, the governor of Alaska, is very attractive as a vice presidential candidate."

But McCain's strongest choice, Carmack said, would be former Arkansas Gov. Mike Huckabee. "Huckabee represents the hard base of the GOP," he said. "He represents the neocons, and it's going to be hard for McCain to ignore that."

And while Carmack said a McCain and Huckabee ticket would "have no problem" appealing to centrist voters, Huckabee would "bring his own constituency" to the race which could prove difficult for McCain.

"The best thing a vice presidential candidate can say is, 'I owe it all to you,'" he said. "And if McCain picks Huckabee, it won't be easy for McCain to control Huckabee in the White House."

Democratic presidential candidate Barack Obama faces similar problems.

Obama, Carmack said, needs to appeal to older, female voters and a female vice presidential candidate would help do that.

"Women over the age of 50 have encountered discrimination," he said. "They have bumped up against that glass ceiling numerous times and that's why Hillary Clinton's candidacy was so strong with that group."

Obama, he said, "has to look at Hillary, there's no question about it."

However, Clinton -- like Huckabee -- could prove difficult to handle. "I don't expect to see a Obama-Clinton ticket," he said.