COLORADO SPRINGS, Colo. (AP) - A group backed by billionaire industrialists Charles and David Koch is investing nearly $4 million in an advertising campaign attacking Democrats in three of the nation's top Senate contests.

The Freedom Partners Action Fund is targeting Nevada, Ohio and Pennsylvania in the television and online advertising blitz.The states are considered top battlegrounds in the fight for control of the Senate this November. Democrats could regain the Senate majority if they pick up four or five new seats, depending on which party wins the White House.Republican incumbents Rob Portman in Ohio and Pat Toomey in Pennsylvania are trying to hold onto their seats, while both parties are fighting for the open seat created by Democrat Harry Reid's retirement in Nevada.Freedom Partners is spending $1.2 million in Nevada airwaves claiming Democrat Catherine Cortez Masto "drove Uber out of Nevada" while serving as state attorney general. In Ohio, another $1.4 million is going to attack former Gov. Ted Strickland's economic record while he led the state. And in Pennsylvania, Freedom Partners is spending $1.3 million charging that Democrat Katie McGinty will look out for "the favored few" if elected."These candidates are promising more of the same," said Freedom Partners' spokesman James Davis in a statement announcing the details.The investment comes as the Koch brothers refuse to invest their tremendous resources in the presidential contest.Charles Koch and his top lieutenants told donors this weekend they would not support Republican nominee Donald Trump, focusing their attention instead on helping the GOP maintain control of the Senate, House and some governorships.Beyond Nevada, Ohio and Pennsylvania, the Koch network is also targeting Senate contests in Florida, Wisconsin and Indiana.