UPDATE: The Walker campaign denies this is true:
The Walker campaign has contacted me to deny this report is true with respect to them. AshLee Strong, National Press Secretary for Scott Walker for America, says the Scott Walker Campaign is not planning any attack ads on Donald Trump.
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Charlie Gasparino reports on Fox News that GOP donors have told him that both Rubio and Walker are planning an ad assault on Donald Trump after labor day in order to ‘reset the primary’. This is sooner than they would have planned to do this, Gasparino says, but it’s becoming critical for them:
Gasparino says they aren’t coordinating, but I suspect their donors who leaked this to him are certainly coordinating. After all their money is on the line.