At stake is the outcome of the highly charged presidential race, which could have an impact on the state's economy for years to come, along with ballot questions that have put Maryland at the center of broader debates over gay marriage and immigration.
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"What we say could reverberate, really, across the country," said Todd Eberly, a political scientist at St. Mary's College. He predicted the passion surrounding this year's ballot initiatives will spark more referendums in the future. "This will be the new normal," he said.
Candidates and advocates made a final pitch to voters Monday — rallying in all corners of the state, knocking on doors in battleground neighborhoods and unleashing a flurry of last-minute phone calls designed to ensure voters will turn out. In making his own case in favor of the ballot questions, Gov. Martin O'Malley broke into song at an event in Baltimore.
Outside Maryland, President Barack Obama and Republican nominee Mitt Romney campaigned in six states. The incumbent and challenger closed by arguing they could do more to lead the country out of the economic doldrums that have marked Obama's first term.
"This nation is going to begin to change for the better tomorrow," Romney said at a rally in Florida.
"Our work is not yet done," Obama, his voice hoarse, told a crowd outside the Wisconsin Capitol.
Maryland officials were predicting a high turnout at the polls here — about 80 percent, deputy state elections administrator Ross Goldstein said. That is consistent with past presidential election years. More than 430,500 Marylanders had already cast ballots in early voting, nearly double the number who voted before Election Day in 2010.
In addition to the presidential race, Maryland will choose nine members of Congress, including a U.S. senator. Most of those races are not considered competitive, but the 6th Congressional District has captured national attention as Republican incumbent Rep. Roscoe G. Bartlett runs an uphill fight for re-election against Democrat John Delaney.
But it is the state ballot questions that will be a driving force behind today's turnout, Eberly and others said. Voters will decide whether Maryland will join six states and the District of Columbia in legalizing same-sex marriage.
Maryland voters also are weighing whether to allow a sixth casino, to be located in Prince George's County, and the addition of table games at all six gambling sites. They will decide whether some illegal immigrants can pay in-state tuition rates at Maryland colleges and universities. And they will determine whether the state keeps its new congressional map — designed to send a seventh Democrat to the House of Representatives — or if the squiggly-shaped districts are sent back to Annapolis for a do-over.
Individual campaigns have sprung up around each of those issues, emanating from church pulpits and television screens. Actor Brad Pitt, pop star Lady Gaga and New York City Mayor Michael Bloomberg have expressed support for Maryland's same-sex marriage law. Ravens center Matt Birk filmed a video last month stating his opposition. Opponents began a robocall campaign last week featuring Florida Republican Sen. Marco Rubio and 2008 presidential candidate Mike Huckabee.
Airwaves have been jammed with advertising over the gambling question, with the two sides spending more than $87 million in their effort to sway voters.
O'Malley, a Democrat, started his day Monday at a rally for expanding gambling. He stood with state lawmakers and repeated a theme supporters have used in some television commercials: A vote for Question 7 will keep Maryland gambling dollars at home rather than in West Virginia, which hosts a mega-casino.
In a twist on the John Denver classic "Take Me Home, Country Roads," O'Malley sang: "Maryland cash, bring it back — to the place where it belongs."
Opponents, who did not have any public events Monday, have built their campaign around skepticism that the new revenue from gambling will go to schools, as promised.
The governor then drove about half a mile to Federal Hill Park, where he stood with Sen. Ben Cardin — who is up for re-election — to pitch same-sex marriage.
Opponents took a lower-key approach but said they were plenty busy.