Former U.S. Sen. Russ Feingold (left), a Democrat, is challenging Republican Sen. Ron Johnson in this fall’s election. Credit: Journal Sentinel files

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Madison — A day after U.S. Sen. Ron Johnson of Wisconsin spoke at the Republican National Convention, a group affiliated with the conservative Koch brothers pulled more than $2 million in ad time in the Badger State.

The move came a day after the National Senate Republican Committee modified its planned help for Johnson, pushing back an ad campaign that was to start next month until October.

Wednesday's development provides another sign Johnson could get less outside support than had been expected. Johnson faces former Sen. Russ Feingold in one of the most closely watched Senate races in the country.

Freedom Partners Action Fund began an ad campaign in May attacking Feingold about the handling of the over-prescription of opiates at the veterans clinic in Tomah. Freedom Partners is funded by the billionaire industrialists Charles and David Koch.

A spokesman for the group, James Davis, said in a statement it was "realigning" its ad buying strategy "to ensure maximum impact across key Senate races." He made the comment after three Democratic sources that track ad buys confirmed Freedom Partners had dropped $2.2 million in ad time it had reserved in Wisconsin in August and September.

Johnson spokesman Brian Reisinger downplayed the move by Freedom Partners.

"We just had our strongest fundraising quarter ever and the polls show this race tight," he said in a statement. "We are comfortable and confident and believe we have the support to run a winning campaign. The voters already fired Senator Feingold once, and they will reject him again."

Feingold spokesman Michael Tyler said in a statement his campaign is focused on Wisconsinites and "not a couple oil billionaires from Kansas."

"Senator Johnson has always relied on the Koch Brothers and these outside groups to run his campaign for him, so this must come as a disappointment for their model legislator," Tyler's statement said.

Freedom Partners did not respond to requests for comment.

The dropped ads come at a time when Johnson had hoped to get more attention because of the national exposure he was getting from speaking at the convention in Cleveland. Johnson for weeks had said he would not attend the convention but reversed course in recent days.

In a poll this month by Marquette University Law School, Feingold led Johnson 49% to 45% among likely voters.