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Voters in the nation's capital will likely legalize marijuana on Tuesday. Here's what you need to know about the big moment in D.C.:

1. The measure allows people ages 21 and over to possess up to two ounces of marijuana for personal use and grow up to six plants.

2. It does not legalize the sale of marijuana.

3. Public consumption will not be legal, so don't light up in front of the White House.

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4. The law will not go into effect immediately. Congress has special authority over the District of Columbia, which means the measure needs to go through a period of congressional review, even after voters approve it. When the D.C. City Council decriminalized marijuana possession earlier this year, the law did not take effect until four and a half months later.

5. Republicans in the House of Representatives will likely try to block it. One of the most vocal opponents could be Rep. Andy Harris (R-Md.), who unsuccessfully tried to stop the city from passing the decriminalization law.

6. Congressional Republicans could have a hard time rolling back legalization. Even if the GOP takes control of both houses of Congress — as election forecasters believe is likely — Democrats will still have a legislative move at their disposal. They can "filibuster" any Republican legislation in the Senate, indefinitely delaying a vote and requiring a 60-vote threshold to continue with debate.

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7. President Obama could also veto any attempt by Congress to undo D.C.'s law. He's supported the rights of voters in Colorado and Washington to legalize marijuana.

8. Stores selling recreational pot could be on the horizon. Councilmember David Grosso is working on legislation that would tax and regulate marijuana sales in the city, but activists believe the council will move slowly on the issue. Adam Eidinger, the driving force behind the legalization campaign, said he doesn't expect D.C. to approve cannabis sales until fall 2016.

9. In the event that marijuana sales are legalized, the market in the city could be worth $130 million a year, according to one study.

Ted Hesson was formerly the immigration editor at Fusion, covering the issue from Washington, D.C. He also writes about drug laws and (occasionally) baseball. On the side: guitars, urban biking, and fiction.