Koch brothers pull ad buy backing Ron Johnson

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.