A source close to the Romney campaign said the team has been contacting potential vice presidential candidates, The Hill said.
"I'm not going to talk about the process," Rubio said. "When they make a choice, I'm sure it's going to be a great choice."
Portman said he respected Romney and the process he had for selecting a running mate and "I'm not going to talk about it."
Ryan similarly said, "I'm not getting into it."
A spokeswoman for the Romney campaign declined to comment.
"During the Gore vettings, somebody said to me, 'It's like having a colonoscopy without painkillers,'" Lieberman told The Hill. "I heard they had gone back and read editorials I had written for the Yale Daily News in 1963. They asked very explicit questions."