A Sandburg Stumper

[Rob Wick]

No Googling, please.

In 1948, Carl Sandburg received a letter from a young historian discussing a picture of a particular person associated with Lincoln. In the letter, this historian quoted at length from a letter sent by a third person also associated with Lincoln. The third person wrote the second, "I want your Photograph--I want it at once--There is use in your saying you 'will probably send it to me--'I must have it--I cant do without it and I don't intend to do without it."

To be correct, first, who is the young historian and second, who are the two people involved in the letter?

Best
Rob