Among politically active social conservatives, there’s a remarkably durable myth that Republicans can make inroads with black voters if only they hold fast to hard-line positions on issues like same-sex marriage. That notion cropped up again this week as part of a widely publicized letter to Republican National Committee chair Reince Priebus in which thirteen officials with social-conservative groups threatened that their followers will leave the GOP or stay home in future elections unless the party pledges to continue its staunch line against gay marriage, a stance now widely unpopular in public opinion polls and among many Republican demographics such as those under 50.

The letter, which you can read here, portrays the issue as vital in GOP minority outreach, which they said should “focus on issues where there is mutual agreement like traditional marriage.” (It does not mention that black opinion, once lopsidedly opposed to same-sex marriage, has swung closer in polls to an even split on the issue). To support this claim, it cites real-world examples from three states: Illinois, Ohio, and my own state of Maryland.

On Ohio, the letter repeats longstanding claims that President George W. Bush’s campaign stance on marriage made the difference in his narrow Buckeye State win in 2004. My colleague David Boaz has already examined those claims in this space, and found the evidence surprisingly thin. The Illinois example, for its part, is self-evidently beside the point: the letter correctly notes that some minority elected officials in that state oppose same-sex marriage, but that does nothing to show that any Illinois blacks are ready to stop voting Democratic because of their concern for the issue.

That leaves Maryland. And in the course of analyzing last November’s Maryland vote in some detail, and writing a series of articles on the results of my research, I feel some confidence in saying that no one has been able to offer evidence that the ballot fight over same-sex marriage did the Maryland Republican Party any overall good with black voters in the state.

As I noted in this December article in The Blaze, Prince George’s County in suburban Washington, which has a substantial black majority among registered voters and has won national attention as a microcosm of black political trends, was hard fought territory in Maryland’s Question 6 fight. In the end, the county split about evenly, Question 6 trailing by just 1 point; the measure was carried to a 5‑point statewide win by a strong showing elsewhere in the Baltimore-DC corridor, notably including many Republican suburbs.

Because P.G. is so large and has so many overwhelmingly black precincts, it afforded an opportunity to investigate whether black voters with socially conservative views are any more likely to vote Republican than those with more socially liberal inclinations. Toward that end, I identified those black-dominated precincts with the strongest social-conservative leanings, as measured by the size of the margins by which they disapproved Question 6. If the “GOP minority inroads” thesis was correctly identifying a genuine trend, you would expect to see signs of a healthy black crossover vote for GOP candidates in those precincts. Instead, the black precincts that most strongly opposed Question 6 were also among those where the GOP got buried most completely, with Mitt Romney getting only (in typical showings) 3, 5, or 6 percent of the overall vote. The down-ticket Maryland GOP candidates, who all happened to be strong social conservatives, were getting beaten just as decisively, including in Senate and House races where all the relevant candidates were white. The GOP’s social-conservative senate hopeful, for example — who ran well enough to carry 13 of 23 counties statewide against lackluster white liberal Sen. Ben Cardin — did even worse in P.G. than Romney, winning only 6 1/2 percent of the vote county-wide and a good bit less than that — as little as 2 percent in one precinct — in the most socially conservative black P.G. neighborhoods.

Republicans who imagine that catering to the most vehement social conservatives within the party will result in a harvest of new black votes are deluding themselves.