Brian J. Tumulty

USA TODAY

WASHINGTON — Donald Trump and Hillary Clinton are positioned to solidify their status as presidential front-runners in Virginia when Republicans and Democrats cast ballots in the state's primary on Tuesday.

Clinton leads Vermont Sen. Bernie Sanders in the Democratic nomination race by 20 points in the swing state. Among Republican presidential candidates, Trump is ahead of his nearest opponent, Florida Sen. Marco Rubio, by 13 points in the latest poll of almost 1,200 voters released Sunday by CBS News/YouGov.

Registered voters in Virginia may vote in either primary (but not both), meaning the state's Super Tuesday nominating contests could serve as a proxy for the November general election. Virginia has no official party registration. Polls are open from 6 a.m. 7 p.m. around the state, and a photo ID is required to cast a ballot.

The Republican candidates will battle over 49 delegates. Thirteen names will be on the ballot, including many who have dropped out of the race.

Clinton and Sanders will battle for the largest share of 95 delegates.

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Republican delegates will be awarded based on results in each of the state's 11 congressional districts. Runners-up can pick up delegates based on their proportion of the vote in each congressional district.

Democratic delegates will be awarded based on results both by congressional district and statewide. The number of delegates at stake ranges from three in one southwestern Virginia district to eight in two Democratic-leaning districts represented by Democratic Reps. Bobby Scott and Don Beyer.

Forty-one percent of Virginia voters said in the most recent poll they plan to cast ballots in the Democratic primary Tuesday, compared with 29% who plan to vote in the GOP primary.

John Whitbeck, chairman of the state Republican Party, said he doubts there will be many instances of Democrats or Republicans voting in the other party’s primary because too much is at stake in each contest.

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In 2008, the last time both parties had contested presidential primaries, 986,203 people voted in the Democratic primary (won by Barack Obama), compared with 489,212 who voted in the GOP primary (won by Arizona Sen. John McCain).

Virginia Democratic Party spokeswoman Emily Bolton expects high turnout again this year.

“We are definitely encouraged,'' she said. "We are seeing a lot of enthusiasm from our folks.’’

Clinton averaged a 19.6-point lead over Sanders in five Virginia polls conducted in February, according to RealClearPolitics. In the two most recent polls — by CBS/YouGov and Monmouth College — Clinton led Sanders by 20 points in one and by 27 points in the other.

On the Republican side, four polls conducted in February show Trump leading with an average 36.8% support, followed by Rubio with 22.3%, Texas Sen. Ted Cruz with 17.5%, Ohio Gov. John Kasich with 7% and retired neurosurgeon Ben Carson with 6.5%, according to RealClearPolitics.