Browning said courts have split on the constitutionality of contribution bans aimed at the gambling industry. He said such bans were upheld in Louisiana, New Jersey and Michigan but thrown out in Pennsylvania. He said he believes such a ban would be upheld in Maryland.

Certainly casino interests have not been shy about using their money to try to advance their interests in Maryland.

William Rickman, owner of the Ocean Downs racetrack and casino, has been giving on a large scale for the last decade. He, along with family members and affiliates, gave almost $400,000 from 2003 to 2007. Penn National, owner of the Hollywood Casino in Perryville and a potential casino site at Rosecroft Raceway, is a politically active donor as well.

Other companies have found routes to cultivate political allies that even O'Malley's strict version of the ban wouldn't have touched. Caesars has given $150,000 to the Democratic Governors Association — which O'Malley heads — since December 2011, according to IRS records. Such gifts are not affected by state laws.

While the courts in recent years have in many cases loosened controls over political donations, the Maryland attorney general's office has taken the position that banning contributions to candidates by members of a regulated industry is within the General Assembly's power.

"Courts more often than not have upheld contribution limits for members of a regulated industry," Assistant Attorney General Sandra Benson Brantley wrote in response to a lawmaker's inquiry last week.

"Although some courts have struck contribution limits as unconstitutional where the ban was overbroad or where there was no indication of a history of corruption or impropriety involving the impacted industry, the bill provisions at issue here are narrowly tailored and targeted to address sufficient state concerns."

Comptroller Peter Franchot, a Democrat who has been critical of O'Malley, said even the originally proposed limits were too little, too late to curb the influence of gambling interests in Maryland.

"Those horses already left the barn a long time ago, and closing the door with this prospective ban on campaign contributions is laudable, but it is preposterous to think it can solve the problem," he said.

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