Sen. Ron Johnson criticized a "false hit piece" about his attendance at hearings.
The group accuses Johnson of ignoring whistleblowers regarding issues at a VA facility.
The internal Harris polling indicates Sanchez could be eliminated before general election.
He announced his decision a day before Maryland's filing deadline.
He was $1 million shy of his Democratic competitor's fourth quarter haul.
The total is reached after raising $3 million in December.
The super-PAC supporting a Democratic underdog bid for Senate is spending most of its haul on the buy.
He raised twice the amount of one of his Democratic Senate opponents.
The ads are part of a $1.5 million national digital campaign launched last month.
Keith Laing 01/28/16 10:36 AM EST
The union is backing Van Hollen over Rep. Donna Edwards in the state's Democratic primary....