"It's not Mike Busch or even the governor. The governor just wants it out of the way," Pinksy said.

For the most part, the governor has explained his support for a special session in terms of settling the issue so it doesn't wreak havoc on another regular session. When the idea of a special session on gambling was first raised, O'Malley said he wouldn't call one until there was a House-Senate consensus on the matter. Yet even as lawmakers are poised to vote, it remains uncertain whether the chambers are fully in agreement.

Many lawmakers would have been willing to accept a deal permitting table games and expanding casino hours as a way to raise revenue — while keeping gambling only at the five currently authorized casino sites. When two Baltimore delegates raised that idea at a meeting last week, veteran Del. Maggie McIntosh – a committee chair and a top ally of Busch – bluntly explained the political realities.

"We have a president of the Senate who will not pass table games unless we have a sixth site," she said.

In recent years, Miller has benefited from industry contributions to his campaign fund, which he employs largely to help Democratic senators in tight races. Since 2003, he has collected at least $100,000 from companies and individuals with direct interests in the gambling industry. In his most recent report, for 2011, Miller reported at least $37,000 from gambling interests – almost 10 percent of his total receipts for that year.

Miller has also received at least $70,000 since 2003 from organized labor — especially the building trades and hotel unions that hunger for the jobs a National Harbor casino would bring.

Eberly said that while there has been speculation about campaign money as Miller's motivation, he believes it might have more to do with the Senate president's roots in Southern Maryland, an East Coast gambling hotbed until the 1960s. At 70, Eberly noted, Miller is one of the few politicians with a memory of the money the gambling halls along U.S. 301 brought to the region.

In his eagerness to foster casino development, Miller was willing to cut a much more favorable deal with the operators than the House was willing to accept. A bill approved by the Senate this spring would have cut the tax on slot machines from 67 percent to 52 percent, partly to offset a transfer of the cost of the machines from the state to the operators. The bill would have set the rate on table games at 10 percent.

O'Malley's bill, in part reflecting tougher bargaining by Busch, offers less generous terms to the larger casinos and requires that some revenue from a tax break be plowed back into the business. In the governor's bill, operators would pay a 20 percent tax on table games.

Eberly said he believes the special session will produce a deal – largely because the governor and Senate president both need one. If they don't succeed, he said, it would look bad for both men. If Busch lets delegates vote their conscience and comes up short, he has less to lose but could face some contention in the future, Eberly said.

"If in the end the House isn't there, certainly any discussion of there being no love lost between Busch and Miller is accelerated to the nth degree," Eberly said.

Baltimore Sun reporter Annie Linskey contributed to this report.