"When we first began planning the march, there was a concerted effort by the Kennedy administration to get it called off and to not let it take place," said Horowitz, who was in charge of organizing transportation for the event.
Holmes Norton, who helped Horowitz with transportation planning, said march organizers "heard nothing but complaints from the Kennedy administration at the time."
"They didn't say, 'Welcome to Washington, this is what I need. If you come to Washington, this will help me get the bill passed,'" she said, referring to Kennedy's proposed Civil Rights Act. "It was quite the contrary."
But as the Kennedys began to see the need for a successful and peaceful march, attitudes began to shift.
If you can't beat 'em, join 'em
The March on Washington organizers envisioned a two-day event that would take marchers around the White House and then to the National Mall, Horowitz recalled.
But she said the Kennedy administration squashed that idea.
"The White House absolutely did not want that to happen," Horowitz said. "And they were able to convince people not to do it."
As a result, the march ended up only being one day, and marchers traversed the mall, not past the White House or Capitol Hill.
The White House had moved past its initial opposition to the march. Robert Kennedy's Justice Department started engaging the march planners, rather than trying to stymie them.
"They kept a watchful eye on the planning of the march," said Lewis, one of the "Big Six" original leaders behind the march. "They stayed in touch with the (march) leadership."
The march leaders, in an attempt to broaden the appeal of the event and widen the scope of its leadership, added four white leaders, changing the "Big Six" to the "Big Ten." They included representatives of the Protestant, Jewish and Catholic faiths, and a labor leader.
Staunch civil rights advocate and United Auto Workers president Walter Reuther was recruited by the White House "to infiltrate the march and steer it away from radical rhetoric and direct action," wrote Charles Euchner in his book "Nobody Turn Me Around," about the historic march.
"And so he did."
By this point, Kennedy had come around so far on the march that, according to march planner Courtland Cox, the president figured if you can't beat them, join them.
"There was a proposal on the table that Kennedy speak to the March on Washington," said Cox. "And (march organizer) Bayard (Rustin) knew this would have been a disaster because it would've been taken over by (Kennedy) just because he's president.
"It would've been Kennedy's march."
So, Cox said Rustin and he excused themselves from that particular meeting and took a walk to the bathroom. Clearly flummoxed about the problem, Rustin took a sip from his back-pocket flask and came up with an idea on the fly.
"And Bayard got back into the meeting and he literally made this up," Cox recalled. "He said that he heard ... if the president spoke the Negroes were going to stone him."
After that, the idea of Kennedy speaking at the march was never considered.
'He was like a beaming, proud father'
Jack Rosenthal remembers the buzz of activity inside the Justice Department's room 5110, Robert Kennedy's office, on Aug. 28, 1963.
"That was the command center," said Rosenthal, who was the department's assistant press officer at the time.
The attorney general was nervous that a disastrous or violent march would hurt his brother's civil rights legislation, and the civil rights cause in general.
Justice Department officials were relying on various eyewitness reports to feed information back to them.