Earlier Thursday, the president called Mandela “my personal hero” and said the former South African president's legacy “will linger on throughout the ages.”

Asked if Mandela's illness would at all change the tone of the president's trip or remarks, Rhodes said only that he expected the president to express his "deep and profound respect for Nelson Mandela." He also said Mandela's declining health would "add significant amount of profundity" to the Robben Island trip.

South African President Jacob Zuma's office said earlier Thursday that doctors reported that Mandela's condition remained critical but was now stable, an encouraging sign for the 94-year-old leader. But Mandela's daughter Makaziwe said in a radio interview with SABC on Thursday that her father's condition “doesn't look good.”

Nevertheless, Makaziwe said, "He's still there."

"He might be waning off, but he's still there."