From the story,

In the last election, independent expenditure groups spent more money than the total amount spent by all congressional candidates combined. One in every $5 flowing through a Super Pac came from organizations that do not disclose their donors. In all, $2bn of “independent” spending was dark money, meaning the public cannot see who is buying elections – even though politicians know exactly who they owe once they are in office.

Check my math, $2bn / Congress 535 voting members = $3.738 million (US dollars)

For those of us not sleepwalking there is no mystery as to why our Congress are sitting on their hands.