Muldowney refused to mention specific concerns he has about Donoghue, whom he called a "nice, fine young man," but said there are issues on which the two differ that he will divulge as the campaign continues.
"It's certainly not going to be a personal or negative campaign in any way," he said.
In recent years Muldowney has been critical of Donoghue, who chairs Washington County's legislative delegation, on several issues.
During one memorable exchange at a county delegation meeting in Annapolis last year, Muldowney scolded the lawmakers, and Donoghue in particular, for failing to pursue amendments to the county's tip jar gaming law. He said they were afraid to revisit the politically sensitive issue and were offering "bogus" excuses for not sponsoring the amendments.
"They pussyfooted around," Muldowney said.
The delegation eventually sponsored the amendments, but were not passed by the full legislature last year. Similar amendments were approved this year.
Muldowney also has been critical of Donoghue for being one of the lawmakers who voted for legislation three years ago that resulted in the city of Hagerstown being saddled with nearly $10 million in debt to the state pension system.
Legislation sponsored by the county delegation during the past two years has reduced the debt by about $5 million.
Muldowney served in the House of Delegates from 1979 to 1986 before losing to current Del. D. Bruce Poole, D-Washington, in a Democratic primary. Since then he ran unsuccessful campaigns for the state Senate and the U.S. House of Representatives. He also has been a member of the Washington County Gaming Commission.
He said beating Donoghue, an eight-year State House veteran, would be difficult.
"It's an uphill battle. I'll be the first to acknowledge it," Muldowney said.
Members of the House of Delegates make $29,700 a year, but are scheduled to receive a raise of $1,809 over the next four years.
The primary election is Sept. 15 and the general election is Nov. 3.