NORTHERN VIRGINIA’S 10th Congressional District is a swing district, won by Barack Obama in 2008 and Mitt Romney in 2012, each time by a narrow margin. Taking in McLean and other wealthy precincts of Fairfax County, all of Loudoun County and other points west past Winchester and Front Royal, it is full of moderate voters. So it’s curious that the half dozen Republicans vying to succeed the district’s longtime Republican representative, Frank Wolf, are engaged in a venomous primary contest to prove which of them is the most hard-line conservative. And it verges on the bizarre when the apparent front-runner, Del. Barbara Comstock (Fairfax), makes a truth-stretching attempt to wrap herself in the mantle of Rush Limbaugh.

Ms. Comstock is among the most conservative lawmakers in Richmond. A lawyer and prolific fundraiser, she represents thousands of commuters in a traffic-clogged district badly in need of road improvements; nonetheless, last year she voted against the first bill in more than a quarter century to provide fresh money for the state’s crumbling highways, even though it was backed by her own party’s top leaders.

Ms. Comstock also supported legislation that would have required women seeking abortions to undergo transvaginal ultrasounds. She backed a measure intended to outlaw abortion by granting individual rights to an embryo from the moment of conception. She voted to repeal a law limiting handgun purchases to one per month. And she opposes expanding Medicaid, which would provide health coverage for up to 400,000 uninsured Virginians.

Despite those stances, and a long record as a Republican lobbyist and loyalist before entering the legislature, she is under attack by GOP primary opponents who consider her insufficiently doctrinaire. Among the criticisms is that, strangely, she voted in Virginia’s Democratic presidential primary in 2008 — for none other than Mr. Obama.

Implausibly, some of Ms. Comstock’s rivals say this proves she is insufficiently conservative. Equally implausibly, Ms. Comstock’s campaign explained publicly that her vote for Mr. Obama was cast at the behest of Mr. Limbaugh, who led an on-air crusade he called “Operation Chaos,” which encouraged crossover voting by Republicans.

One problem with this explanation is that Ms. Comstock apparently believes that sucking up to Mr. Limbaugh, a vicious polemicist with a flair for toxic misogyny, gives her an aura of respectability. Another problem is that it’s untrue.

The 2008 Virginia presidential primary in which Ms. Comstock cast her vote was held on Feb. 12. But according to Mr. Limbaugh’s own online archive, his earliest on-air reference to “Operation Chaos” was two weeks later — when he urged a crossover vote for Hillary Clinton, not Mr. Obama.

Being a sycophant to Mr. Limbaugh is bad enough; it’s even worse when the sycophancy is based on a fabrication. (In response to our inquiries, Ms. Comstock acknowledged that her “recollection” was flawed, and that her vote had nothing to do with Mr. Limbaugh. She said she voted for Mr. Obama because she thought he’d be the easiest candidate for a Republican to beat in the general election.)

Ms. Comstock’s past primary votes are her business. But by jockeying to appeal to the most extreme fringe of the electorate, Republicans run the risk of alienating centrist, level-headed and educated voters in the 10th District.