"He also deserves the lion’s share of the credit for producing the durable Camp David Accords. Carter, an Annapolis grad, has always loved his country," Shirley, who has written four books on President Reagan, added.
Carter, 98, has been widely praised for his "second act" after leaving the White House and dedicating himself to helping others through charity and promoting diplomacy around the globe.
ON THIS DAY IN HISTORY, JAN. 21, 1977, PRESIDENT CARTER PARDONS VIETNAM WAR DRAFT DODGERS
On Saturday, The Carter Center announced that the former president will spend time at home rather than receive "additional medical intervention."
"He has the full support of his family and his medical team," the center's statement said. "The Carter family asks for privacy during this time and is grateful for the concern shown by his many admirers."
PRESIDENT JIMMY CARTER HOSPITALIZED FOR PROCEDURE TO REDUCE PRESSURE ON BRAIN AFTER RECENT FALLS
Well wishes immediately began pouring in on social media following The Carter Center's announcement.
"This man moves humanity forward every single day," Maria Shriver, a journalist, philanthropist, and niece of former President John F. Kennedy, posted on Twitter. "He is such an inspiration. Devoted his whole life to public service. Sending him and his family my love, my respect, my support."
Jason Carter, the former president's grandson who now chairs The Carter Center governing board, said Saturday in a tweet that he "saw both of my grandparents yesterday. They are at peace and—as always—their home is full of love."
Carter celebrated his most recent birthday in October with family and friends in Plains, Georgia, the tiny town where he and his wife, Rosalynn, were born in the years between World War I and the Great Depression.
The Carter Center last year marked 40 years of promoting its human rights agenda.
The Associated Press contributed to this report.