It is what you call a "a coup d'etat."

[IScreamSundays]

Jim Garrison, the New Orleans District Attorney who prosecuted Clay Shaw for conspiring to murder Kennedy, claimed to have discovered the "changed route." He says that, during his investigation of the assassination in 1967:
The temporary respite from the investigation did not last long. Frank Klein could not stay away from it, and neither could I. One morning I was in my office reading and rereading a newspaper. I did not hear Frank enter.
"I have never seen you so preoccupied," said Frank.

"It's not just any paper, son," I said. "This is the front page of the Dallas Morning News for November 22, 1963."

"Well, what's got you so hypnotized?"

I gestured to the large diagram on the paper's front page, indicating the route of the presidential parade. "Have I ever shown you this before?" I asked.

He shook his head.

I turned the paper around facing his way so that he could read the diagram of the motorcade. It covered almost five-sixth of the front page.

"Frank," I said, "I want you to follow the parade route with me. Let's pick it up right here as it comes down Main approaching Dealey Plaza. Are you with me?"

"Yes," he said, his finger following the thick line indicating the motorcade. "And here is where it reaches Dealey Plaza . . . " He stopped.

"What's the matter?" I asked.

"This diagram indicates that the President's parade was supposed to continue on Main Street through the center of Dealey Plaza -- without even leaving Main." He stared at it in disbelief.

"So what's wrong with that?" I asked.

His finger was moving off of Main, inches downward to Elm until he found the Depository area where the President had been shot. "If that was the presidential parade route up there on Main . . . "

I finished the question for him. "How did he get way down here on Elm?"

Frank looked up at me with a slight frown, then looked back at the diagram. He moved his finger back along Main Street to where it reached Houston. "The motorcade turned right on Houston and went down onto Elm," he said. . . . "Here on Main Street, continuing through the open meadow," he said, "they couldn't have hit him. Are you telling me that at the last moment they just moved the President of the United States off of his scheduled route to here where the Depository is?" He pushed back his chair and stood up. "Hell, I haven't read a damned word about that anywhere. How can they keep something like that a secret for three years?"

<...>

Frank grabbed the front page of the Dallas Morning News and pointed to the diagram. "Hell," he said, "was the Warren Commission blind? Didn't they see this?"

"Oh," I said. "Would you like to see the front page that was introduced to the Warren Commission?"

I pulled open my middle desk drawer and took out a copy of the Dallas Morning News front page that had been introduced as a Commission exhibit. I handed it to Frank and lit my pipe. I had hardly taken the first puff on it when he yelled.

"Those bastards! They just removed the entire motorcade route from the front page."

That was true. On five-sixths of the Dallas Morning News page where the diagram of the motorcade route was supposed to be was nothing but a large square of solid gray. "And this has been printed as an official exhibit by the Warren Commission?" he asked.

I noded.

"And just what in the hell are we supposed to call this?" he asked, waving the nearly blank exhibit.

I took a puff or two on my pipe. "This is what you call," I replied, "a coup d'etat."

On the Trail of the Assassins, pp. 101-103.

So the very sage, very perceptive Garrison caught the Warren Commission in a "coverup" of a key piece of evidence. According to Garrison.

[SDuderstadt]

1. JFK got "way down there on Elm" because...

the next stop was a luncheon at the TradeMart, which required the Motorcade to take the Stemmons freeway. The motorcade could not continue on Main and make the turn onto the Stemmons Freeway.

Duh.

[NYMdaveNYI]

5. According to a poll....

80% of Americans believe JFK’s assassination was a conspiracy......


Apparently the other 20% are still part of the conspiracy.

[deconstruct911]

6. 19% of that 20% just have their head in the sand.nt

[SDuderstadt]

7. We're just waiting for you to....

bust this thing wide open, dude.

[k-robjoe]

2. McAdams

Have to agree with SDduderstadt here.

You are quoting McAdams. Here is the link :

http://mcadams.posc.mu.edu/route.htm

It makes Garrison look silly.

[k-robjoe]

3. That said

There were apparently alternative routes :

"In a related matter, the motorcade route itself went against both common sense and Secret Service protocol by involving turns of 90 and 120 degrees, which slowed the limousine down to a dangerous speed by both the Texas School Book Depository (Oswald's alleged lair) and the infamous grassy knoll area --- DNC advance man Underwood and uniformed agent Norris were two men who strongly criticized the route in interviews with this author. Furthermore, the #1 agent in the president's detail, Jerry Behn, told me that the Dallas route was changed from some other (unknown) choice, as the House Select Committee on Assassinations asked him in Executive Session in still unpublished testimony in the late 1970s. Furthermore, agents Kinney and Winston G. Lawson confirmed for this author that there were indeed alternate routes (two, according to Kinney), and the author discovered much confusion in the newspapers and perhaps unwitting obfuscation in the strangely conflicting accounts of the route Kennedy was to take in Dallas."

http://mcadams.posc.mu.edu/palamara/factsheet_vmp.html

[OnTheOtherHand]

4. especially the bit about "almost five-sixths of the front page"

Vivid writing, but it's more like "almost one-twentieth."