In one document he scribbled a picture of a bullet piercing the head of his chief of staff.
In another, he wrote the word "Nixon" next to a whip. One can only imagine what was going through his head at the time.
Greenberg is sensitive to accusations that presidential doodlers are weak-minded men.
"People think of doodles as a sign of a mind wandering, but really there can be something disciplining about doodling," Greenberg said. "It can be a way to focus your mind. Sometimes it's when you're not necessarily dwelling on your problem at hand that you come up with solutions."
He believes that's the case with President Johnson.
Johnson frequently drew scribbles over the words "The White House" that adorned the top of his stationery.
Greenberg believes it's a habit the president developed to calm his mind.
There is another possible interpretation of those doodles.
"The Johnson under the strain of Vietnam and the party turning on him was a man full of anger and resentment. And there are times he drew bars over the words 'White House,'" Greenberg said.
"It's going too far to say he saw the White House as a prison, but certainly by the end of his presidency he was unhappy there."
The Johnson sketches also include two pages of tight lines drawn in precise quilt patterns, and Greenberg sees the sketches as an important reminder of Johnson's skills.
"We remember Johnson as someone who was given over to urges all the time, but he was also enormously successful. There was no one more methodical in executing a plan. And it's nice to be reminded of that side of Johnson, which we see in these sketches."
Reagan was one of the more prolific presidential doodlers.
His sketches are interesting for what they don't reveal.
They betray no anxieties or internal struggles.
Instead, he sketched happy cartoonish pictures of cowboys and costumed movie characters often accompanied by love notes to his wife.
He filled one piece of paper with scribbled heads, including one that looked like his wife, Nancy, along with a heart pierced by an arrow.
It also was inscribed with his and his wife's initials, and a note read: "There I was doodling away -- then I began to think about you."
Greenberg says Reagan loved to give away his doodles as "as an instrument of public relations."
Greenberg said, "For him, the doodle was a deliberate way to show off his lighter, endearing side. There's a calculated side to Reagan's doodles."
Most other presidents were not as forthcoming with their silly scribblings.
The book's introduction starts with an anecdote -- recalled by former White House counterterrorism czar Richard Clarke -- about President Clinton doodling during a meeting about the Somalia crisis.
Apparently Clinton was a doodler.
The former president, whose papers are still private, did not turn over any doodles for the book.
President Bush also did not turn over doodles.
The authors included the only private scribbling available from the current president -- a note that Bush wrote to Secretary of State Condoleezza Rice during a meeting of the United Nations.
It reads: "I think I may need a bathroom break? Is this possible?"
It's not a favorite moment for the current White House so perhaps a doodle would have been less embarrassing.
Greenberg understands why the presidents don't want their scribbles made public.