Paperless voting machines are a glaring weakness in U.S. election infrastructure.
Experts say they are dangerous because they lack paper voting records.
Politico reports the machines are vulnerable to malfunctions or intrusions that could undetectably change votes.
Top U.S. intelligence officials are predicting the return of Russian hackers in 2020.
What is preventing counties across the US from upgrading their voting machines?
Many counties do not have the money to upgrade voting machines.