At first, Maryland lawmakers were leery of full-fledged casinos. In 2007, after years of debate, they settled on allowing five casinos with only slot machines, and they made sure voters had the final say in a constitutional amendment in 2008. It took Tuesday's statewide vote four years later, however, to fully open the door to casinos with all the offerings after the most expensive political advertising campaign in Maryland's history.

"It's kind of a grand culmination of Maryland's casino venture," said James Karmel, a professor of history and a gambling analyst at Harford Community College. "It has been a long time coming."

Prince George's County Executive Rushern Baker, who worked to build support for a casino near Washington, said National Harbor could rival Atlantic City, N.J., and even some places in Las Vegas. That's because the 300-acre waterfront development that opened in 2008 already has hotels, restaurants, shopping and a convention center.

"I think it will make us a premier destination place for entertainment, and that's really what this is about -- not only, as I said, the table games and the slot machines but also the high-end entertainment, the shops, the restaurants," Baker said at a news conference Wednesday. He said he expected it would attract people who come to Washington to attend conferences and tour the nation's capital.

Voters approved Question 7 with 52 percent of the vote.

The relentless advertising campaign by gambling companies underscored how lucrative they view the market around the District of Columbia. More than $90 million was spent, mostly by two companies.

Penn National Gaming Inc., which owns a large casino in Charles Town, W.Va., near Maryland's border, charged in front early to oppose the ballot question. Las-Vegas based MGM Resorts International, which wants to build an $800 million casino and resort at National Harbor by the Potomac River in Prince George's County, caught up with big spurts of spending in the waning days of the race.

Hollywood Casino at Charles Town Races & Slots, which stands to lose revenue when the new casino opens in Prince George's County, has easily been West Virginia's strongest-performing racetrack.

Hollywood Casino had been providing the lion's share of state casino revenues, thanks to a location unaffected by competition from Ohio and -- until Tuesday -- had only been minimally impacted by video slots in neighboring Maryland.

In August, Charles Town produced $13.3 million in table games revenue for the month -- more than three times the $4.2 million of revenue from the three other racetracks and The Greenbrier casino combined.

"Starting today, MGM's talented team of designers and resort experts begin work on our proposal for a great destination resort for the people of Prince George's County and the state of Maryland," Jim Murren, MGM's CEO, announced Wednesday. "We stand ready to compete with all comers for this license and the privilege to bring an MGM resort to National Harbor."

The casino planned by MGM would have up to 3,000 slot machines, as well as table games.

The Prince George's County casino can't open until 2016. Table games could arrive at Maryland's three existing casinos sometime next year and at two other casinos when they open. Caesars Entertainment was awarded a license earlier this year to open a casino in Baltimore. It has been scheduled to open in 2014. A casino in western Maryland at Rocky Gap State Park is planned to open next summer or early next fall.

Voters who supported the ballot question on Tuesday cited the importance of keeping gambling revenue in Maryland, instead of allowing it to flow to neighboring states like West Virginia, Delaware, Pennsylvania and New Jersey. Supporters also noted job creation as a key factor in their decisions. While opponents said they voted against the expansion because they doubted a significant amount of the state's proceeds from gambling would go to education as promised, supporters said it's hard to argue with the fact that the state needs the jobs and money.