Then-Del. Mark Dudenhefer in 2013. (Bob Brown/Richmond Times-Dispatch via Associated Press)

REPUBLICANS IN Richmond have gerrymandered Virginia so thoroughly that they control two-thirds of the 100 seats in the House of Delegates even though the state is as purple as they come. One result is that tens of thousands of needy Virginians are condemned to live without health insurance, for which they would be eligible, and which would be paid for with federal funding, if the state legislature would expand Medicaid — which it won’t, owing to the logic-defying refusal of nearly every GOP lawmaker.

Still, the state party remains split between pragmatists and doctrinaire conservatives, as it has been for years, and it is critical that the former continue to hold sway if the legislature is to retain its traditions of moderate, pro-business governance.

The legislative elections are Nov. 3. Beginning today, The Post’s endorsements in Northern Virginia’s most competitive House races will appear in bold type; more will appear in a subsequent edition. (Our picks in the region’s key state Senate races appeared earlier.)

To determine your legislative district and candidates on your ballot, go to .

District 2. Republican L. Mark Dudenhefer , a one-term delegate who lost this seat in a closely contested race two years ago, is running to regain it after the departure of an incumbent who ran for the state Senate. A retired Marine officer and former chairman of Stafford County’s Board of Supervisors, Mr. Dudenhefer is a constructive conservative unafraid to cross partisan lines when it makes sense — as he did in joining Democrats (and other moderate Republicans) to back a major transportation funding package in 2013. His Democratic opponent, Joshua L. King, an Army veteran and sheriff’s deputy in Fairfax, is a novice whose grasp of public policy is tenuous.

District 13. It’s conceivable there are more extreme and incendiary lawmakers in Richmond than Del. Robert G. “Bob” Marshall, but if so, it’s a brief list. Mr. Marshall, a Republican widely known as “Sideshow Bob,” spews contempt for the disabled, for gay men and lesbians, for women who have abortions and for anyone else who does not match his cramped ideal of a perfect society. Even fellow Republicans roll their eyes at Mr. Marshall’s off-the-wall philosophizing.

He has suggested that God’s vengeance explains disabled children born to women who previously had abortions; tried to ban gays from serving in Virginia’s National Guard; proposed that the state establish its own currency lest the Federal Reserve collapse; and led an assault on climate-change science by attacking academic freedom at the University of Virginia. He accepted campaign contributions exceeding the legal limit when he ran for Congress last year, then ignored federal regulators who warned his campaign about the violation.

A much better choice is Democrat Donald B. Shaw , an Army and Air National Guard veteran and defense contractor who would be a sober, serious advocate on transportation and veterans issues. Unlike Mr. Marshall, Mr. Shaw would stick to the concerns of his constituents in Prince William County — and to the facts.