Former vice president Joe Biden has waded into one of the most watched statehouse races in the country, endorsing a Prince William County Democrat who is trying to oust a longtime incumbent and become the first openly transgender individual elected in Virginia.

Biden, who has called transgender rights the "civil rights issue of our time," issued a statement Monday in support of Danica Roem and four other Democrats running for the House of Delegates in November, part of a push by the state party to end or weaken the Republican Party's 16-year dominance in the chamber.

The statement emailed to Virginia's Democratic Party cited Roem's focus on transportation, including ways to improve traffic-clogged Route 28.

"As someone who spent decades riding the train to work, I'm proud today to endorse Danica Roem's historic candidacy, because I know her emphasis on improving transportation infrastructure is critical to improving the quality of life for thousands of Virginians," Biden said.

"I know she'd make people of her lifelong home of Prince William County proud by working to improve their commutes and strengthen the middle class while serving them with compassion in Richmond and Manassas."

Roem, who is in a heated battle with Del. Robert G. Marshall (R), declared herself "humbled" by Biden's endorsement.

"I have made transportation policy my top priority," she said. "This helps us entirely."

Biden campaigned in Northern Virginia last weekend for gubernatorial candidate Ralph Northam (D), currently the state's lieutenant governor. He also endorsed four other Democratic state House candidates: first-term incumbent Del. John J. Bell of Chantilly, a 26-year Air Force veteran who faces Republican challenger Subba Kolla; Jennifer Carroll Foy, who is running against Republican Michael David Makee for the open House District 2 seat in Prince William County; David Reid of Ashburn, who is challenging Del. Thomas A. "Tag" Greason (R) for the House District 32 seat; and Elizabeth Guzman, who is challenging Del. L. Scott Lingamfelter (R) in House District 31.

Biden called Bell "a proven leader . . . [who] has a track record of getting things done across the aisle and advocating for his constituents."

Republicans have a 66-to-34 majority in the House, and all 100 seats are on the ballot Nov. 7.

According to the latest campaign finance filings, Democratic House of Delegates incumbents, challengers and leadership PACs raised $5.7 million through September, while Republicans raised $3.6 million.

View Graphic Virginia general election guide

But Republicans are sitting on an enormous treasury, built up over years: They had $8.4 million in accounts heading into October, according to an analysis of the latest data by the Virginia Public Access Project, while Democratic House candidates had $5.1 million.

Roem, who has raised nearly $500,000 in 2017, lost her cash-on-hand edge to Marshall in September after spending more than $200,000, including on two ads. She ended the month with $78,000 available.

Marshall, who had raised about $50,000 through August, picked up his fundraising pace in September, taking in $82,103, including a $20,000 check from the chairman of a group that opposes transgender rights. He ended the month with $173,000 available.