I had been under the impression that a cyanide poisoning was not quick, but somewhat slow and agonizing. This sounds like he was dead before hitting the ground. Especially since the guy said he didn’t notice him in any distress; he just fell over. Maybe some of the medically trained on here can tell us what happens with a sudden aortic dissection.
If he was showing no signs of distress, was "dead before hitting the ground" & his skin color was "bright red," does a sudden tear in the aorta fit this description?
"Sudden severe chest or upper back pain, often described as a tearing, ripping or shearing sensation, that radiates to the neck or down the back
Loss of consciousness (fainting)
Shortness of breath
Sudden difficulty speaking, loss of vision, weakness, or paralysis of one side of your body, such as having a stroke
Sweating
Weak pulse in one arm compared to the other
[1] [2]...When to see a doctor If you have signs or symptoms such as severe chest pain, fainting, sudden onset of shortness of breath, or symptoms of a stroke, call 911 or emergency medical assistance."
And...
"Symptoms
Virtually everyone who has an aortic dissection experiences pain—typically sudden, excruciating pain, often described as tearing or ripping. Most commonly, the pain is felt across the chest but is often also felt in the back between the shoulder blades. The pain frequently travels along the path of the dissection as it advances along the aorta.
As the dissection advances, it can close off the points at which one or more arteries branch off from the aorta, blocking blood flow. The consequences vary depending on which arteries are blocked. Consequences include stroke (if the cerebral arteries, which supply the brain, are blocked), heart attack (if the coronary arteries, which supply the heart muscle, are blocked), sudden abdominal pain (if the mesentery arteries, which supply the intestines, are blocked), lower back pain (if the renal arteries, which supply the kidneys, are blocked) and nerve damage that causes tingling or an inability to move a limb (if the spinal arteries are blocked)."
Those symptoms don't seem to fit what happened to Breitbart.
In the quick searching I've done, I wasn't able to find anything that indicated that ones skin would...or even might, turn a more reddish color after suffering from a tear of the Aorta.
Additionally, it doesn't sound like a tear would cause someone to drop like a sack of potatoes and never regain consciousness.
OTOH, a massive aortic aneurysm certainly has the potential to drop someone like that. However, if that were the cause, his skin color would be pale (etc.), but not "bright red."
The coroner is waiting several weeks for the results of toxicology test(s) to come back, to make sure they "cover all the bases."
I'm thinking that a physical tear or bursting of his aortic artery would not require toxicology results. That would be readily observed and no doubt reported within days. At least, in a preliminary report.
The circumstances, the eye witness account, the rush to call this "natural causes" before a cause of death is known...does seem highly suspicious.