Republicans are deeply concerned about how to run against Barack Obama this fall should he be the presidential nominee for the Democratic Party, and they are right to be apprehensive. If John McCain were to belittle the accomplishments of Dr. Martin Luther King Jr., as Mrs. Clinton did, it would be deemed proof positive of deep-seated Republican racism, not written-off as mere campaign clumsiness.

No white politician of this age has been more widely received by African Americans than Mrs. Clinton’s husband, William Clinton, and even he has been criticized for certain comments about Mr. Obama. New York Attorney General Andrew Cuomo came under fire for his “shuck and jive” comment, which was simply a case of poorly chosen words.

Other supporters of Hillary Clinton have made more blatant racial blunders, as when William Shaheen implied that, based on Mr. Obama’s admitted past drug use, he might have been a drug dealer. Such a charge would likely never be made about a white candidate confessing to an equivalent personal history.

And yet, none of these Democrats suffered damage to their personal or political reputations because the Democratic Party is presumed to be the party of civil rights. Their transgressions are assumed to be simple mistakes and are quickly forgiven by Democratic constituents and the media alike.

These assumptions demand a review. Historically, it is the Democratic Party that has been the party of racism in this country. Its co-founders, Thomas Jefferson and Andrew Jackson, owned large numbers of slaves, and every Democratic president and presidential nominee prior to the Civil War defended slavery without reservation.

The South’s dependable Democratic constituency made it the Democratic Party’s base. Even liberal northern Democrats like Franklin Roosevelt and John F. Kennedy kowtowed to the “Solid South” and avoided pressing Congress to pass anti-lynching legislation and voting rights bills that would risk alienating a region essential to their election.

Yet despite this history of the Democrats’ racial hostility, a majority of African Americans voted Democratic from 1936 onward because Republicans — the party of Abraham Lincoln — had become complacent about the black vote. The Republican Party did little after 1875 to reach out to African Americans directly, winning the bulk of black votes between the mid 1870s and the mid 1930s by default. Meanwhile, African American loyalty to the Republican Party slowly began to erode.

But even after the majority of black voters shifted to the Democratic Party in 1936 — largely due to New Deal relief measures — Republicans still received, on average, 30% of the vote until 1964. That year, the Republican share fell to just 6%. It has averaged only 10% ever since.

Clearly, African Americans were extremely grateful that the Democrat candidate, Lyndon Johnson, pushed the Civil Rights Act of 1964 into law — even if it’s passage required the overwhelming support of Republicans to defeat the opposition of Senate Democrats such as Robert Byrd, who alone filibustered the legislation for more than 14 hours.

If Mr. Obama gets the Democratic nomination, he will undoubtedly take an even higher percentage of the black vote this year than the Democratic nominee normally gets. But if Mr. Obama loses the nomination in deference to Hillary Clinton, Republicans are presented with a historic opportunity to appeal to disaffected black voters who may feel that the nomination was stolen from Mr. Obama. Regardless of whom the Democrats nominate, the Republican Party needs a black outreach strategy. It will take the edge off attacks on Mr. Obama, if he is the nominee, showing that such attacks are not racially based. Even if such a strategy yields no new votes, Republicans still ought to do more to appeal to African American voters.

Not only is it the right thing to do — our great political parties should seek to represent the interests of all Americans, including those who vote against them — but there is considerable evidence that blacks are tiring of being taken for granted by Democrats, who are pocketing their votes while expending time and effort reaching out to the larger and faster growing Hispanic population.

The payoff may not come this year if Mr. Obama is the Democratic nominee. But even if a black outreach effort serves only to blunt the perception that Republicans would rather appeal to whites still flying the Confederate flag than African Americans — then that’s a step in the right direction.

Such a strategy may prove fruitful in unexpected ways: Republicans could pick up votes from moderates previously uncomfortable with the party’s indifference to black concerns.

Mr. Bartlett is the author of “Wrong on Race: The Democratic Party’s Buried Past.”