The brothers are known for bankrolling conservative candidates and causes.
Freedom Partners is a group closely linked with the Koch Brothers and Andrew Zucker with the Jeff Merkley campaign says the are funding a lot of buys for Wehby.
"The campaign has media trackers that track these things real time. And at the end of last week, they bought 1.5 million in cable in Oregon and as of right now the Koch Brothers have funded a total of upwards 3.1 million dollars."
Recent filings with the Federal Election Commission show that Merkley has raised about twice as much money from April through June as Wehby did.