The ad, which ran twice on the WBAL-AM radio program Saturday, says Ehrlich must be living in a "fantasy land" to say he left office with hundreds of millions of dollars in budget surplus.
Ehrlich talked about the ad after it aired. He questioned why O'Malley's campaign would run the ad at a time when the state Democratic party is contending that program sponsors are in effect subsidizing Ehrlich's campaign.
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Ehrlich did not address the ad's message. That's for another time, he said.
The Republican candidate said he plans to keep his radio show until he formally files to run against O'Malley. The filing deadline is July 6.