Fredreka Schouten

USA TODAY

WASHINGTON — The Kochs are jumping back into the Wisconsin Senate battle.

Just weeks after canceling more than $2 million in advertising to help Sen. Ron Johnson's reelection bid, a deep-pocketed outside group affiliated with conservative billionaire Charles Koch and his brother, David, announced Thursday that it is spending $1 million to influence the Senate race.

Freedom Partners Action Fund launched digital ads in the state Thursday and will start television ads Friday.

"We've seen some changes in the polls," Freedom Partners spokesman James Davis told USA TODAY.

The group's decision last month to pull its ads was viewed as an ominous sign for Johnson, a freshman locked in a tight battle with Democrat Russ Feingold, a former three-term U.S. senator. Johnson is considered one of the most vulnerable Republican senators on the ballot in November as his party fights to retain its majority in the chamber. Recent polls have given Feingold the edge.

When Freedom Partners pulled its ads last month, Davis described the decision as a realignment of its advertising strategy across Senate races and said the group still was committed to on-the-ground voter outreach and direct mail in the state.

Thursday, Johnson's spokesman Brian Reisinger said the campaign is strong shape.

"Everyone can see that Ron Johnson is working hard for Wisconsinites and running a race that is earning their support," he said in an email about the Kochs' move. "The choice in Wisconsin is clear: between an Oshkosh manufacturer working to create jobs and keep us safe, and a career politician trying to claw his way back to Washington."

Koch brothers pull ad buy backing Ron Johnson

Charles Koch's network of like-minded donors has plowed hundreds of millions into federal politics in recent years to help Republicans and to push his libertarian-leaning views. But Koch has made it clear that he dislikes the policies of the two major-party nominees for the White House, Republican Donald Trump and Democrat Hillary Clinton, and will concentrate on down-ballot races rather than the presidential contest this year.

Charles Koch donates $3 million to help Senate GOP

The new Freedom Partners' ad slams Feingold as failing to address the over-prescription of opiates at a Veteran Affairs' medical center in Tomah, Wis.

Feingold and Freedom Partners have squabbled over the group's Tomah ads in the past, and Feingold spokesman Michael Tyler said the new commercial is part of a "tired smear" campaign from the Kochs.

"Russ is the only candidate who is actually listening to and fighting for Wisconsin's veterans and their families," Tyler said in a statement.

Here's the ad: