Cain pointed to an article that argues Santorum will have less traction than in 2012.
Donors can win a signed photo of father and son.
The former Maryland governor is expected to launch a presidential campaign this week.
Jones, who sued Bill Clinton for sexual harassment, said Hillary should not be running.
The decision comes ahead of the South Carolina Republican's 60th birthday.
Richard Trumka said support of the TPP would cost Clinton the enthusiasm of organized labor.
"Well, I would expect to hear that from maybe Bernie Sanders," Santorum said.
Paul and Rubio represent the greatest challenge to Clinton, the new poll found.
Alexander Bolton 05/28/15 06:00 AM EDT
Sensing a vulnerability, 2016 contenders are beginning to go after Paul.