Anchored by Jake Tapper, The Lead airs at 4 p.m. ET on CNN.
Former President Jimmy Carter and Rev. Jesse Jackson remember Nelson Mandela.
Letters sent to President Obama and Sen. Roger Wicker, R-Mississippi, have initially tested positive for ricin, a deadly poison. Suspicious packages forced evacuations at Senate offices earlier today.
"Ricin is a byproduct of the caster beans," said Leonard Cole, a terror medicine expert with Rutgers University. When getting caster oil from caster beans, one of the byproducts is ricin.
"When ricin is purified ... and produced in a light powder form that can float and be inhaled, it can be highly dangerous, lethal," said Cole.
"One or two grains of salt would be the equivalent size of the amount of ricin that would be lethal to a human being, if a person ingests or inhales it," said Cole.
There is no antidote.
Ricin is easily available, but has not been commonly used as a bio terrorist agent.
If you have been exposed to ricin, the effects are like a neuro toxin, the poison begins to shut down your nervous system. Symptoms include abdominal pain, dizziness, chest tightness, vomiting, fever, fatigue, and seizures. After awhile, victims have trouble with co-ordination and neurological capabilities, and ultimately die.
"Every step along the way, when we've experienced and confronted the horror associated with these attacks, there have been lessons learned," said former Secretary of Homeland Security Tom Ridge.
In response to the anthrax attacks that happened immediately after the 9/11 terrorist attacks, mail is not sorted at Congress or the White House, but at a separate facility.
While the nature of the attack is serious, Ridge cautions against overreaction.
"It is not a contagion, there are certain symptoms, and right now it seems to be a condition that is well-contained," said Ridge.
The two letters sent to the president and the senator are still being analyzed for the presence of ricin, lab results are expected on Thursday.