On Saturday, news organizations linked Dylann Roof, the sole suspect in last week's Charleston church shootings, to a website with a rambling manifesto of hate, illustrated with dozens of pictures. Several showed him posing with a Confederate battle flag.

The flags of the United States and of South Carolina, atop the Capitol dome in Columbia, were lowered to half-staff last week in the wake of the Charleston shootings. The Confederate battle flag flying on the Capitol grounds was not.

“It’s a shame that those people were killed, and we all greatly regret that incident,” a spokesman for the Sons of Confederate Veterans told The New York Times, “and we were upset that anybody would try to tie people who are proud of their heritage to an act like that.”

But, of course, Roof understood the symbolism of the flag he waved only all too well. When South Carolina seceded in 1860, it issued a Declaration of the Immediate Causes Which Induce and Justify the Secession of South Carolina. It glossed over states’ rights. It did not mention the tariff. South Carolina was seceding, it explained, due to the “increasing hostility on the part of the non-slaveholding States to the institution of slavery,” and the election of a president who believed “that slavery is in the course of ultimate extinction.”

South Carolina’s Declaration was drafted by Christopher Memminger, considered a moderate at the time. So well did he articulate the grievances of the South that he was selected at Montgomery to draft the provisional constitution of the new Confederacy, and then to serve as its treasury secretary.

It was in Charleston, South Carolina that the fiery secessionist Edmund Ruffin fired the first shot of the war. And on June 17, 1865—exactly 150 years before the Charleston attacks—Ruffin learned of the South’s surrender, reportedly wrapped himself in a Confederate flag, and then took his own life rather than accept defeat. Those, like Roof, who now want a secessionist banner of their own can order one from the Ruffin Flag Company.

After the surrender in 1865, Confederate flags were folded and put away. They were most likely to be spotted at memorials or cemeteries. Even after the hopeful decade of Reconstruction gave way to the violent repression of Redemption, open displays of the flag remained rare. There was no need for a banner to signal defiance; Jim Crow reigned unchallenged.

The flag slowly crept back into public life over the ensuing decades, saluted at veterans’ reunions, promoted by the United Daughters of the Confederacy, even carried into battle by units from the South. By the mid-twentieth century, the flags were also waved by football fans, and sold to tourists.

But as a political symbol, the flag was revived when northern Democrats began to press for an end to the South’s system of racial oppression. In 1948, the Dixiecrats revolted against President Harry Truman—who had desegregated the armed forces and supported anti-lynching bills. The movement began in Mississippi in February of 1948, with thousands of activists “shouting rebel yells and waving the Confederate flag,” as the Associated Press reported at the time. Some actually removed old, mothballed flags from the trunks where they had until then been gathering dust.

At the Democratic convention that July, nine southern states backed Georgia’s Senator Richard Russell over Truman, parading around the floor behind a waving Confederate flag to the strains of Dixie. The Dixiecrats reconvened in Birmingham, nominating South Carolina Governor Strom Thurmond for the presidency. Sales of Confederate flags, long moribund, exploded. Stores could not keep them in stock. The battle flag became the symbol of segregation.

The flag soon spread. It fluttered from the radio antennas of cars and motorcycles, festooned towels and trinkets, and was exhibited on both sides of the Mason-Dixon line. Some displayed it as a curiosity, a general symbol of rebellion against authority, or an emblem of regional pride. The United Daughters of the Confederacy were split on how to respond, some pleased to see young people showing interest, others calling the proliferation of flags a “desecration.” Newspapers tried to explain the craze, citing explanations from football fans to historically themed balls.

The black press did not find the phenomena quite so baffling. “In a large measure,” wrote the Chicago Defender in 1951, “the rebel craze is an ugly reaction to the remarkable progress of our group.” That was true in the North, as well as the South.

Over the next two decades, the flag was waved at Klan rallies, at White Citizens’ Council meetings, and by those committing horrifying acts of violence. And despite the growing range of its meanings in pop culture, as a political symbol, it offered little ambiguity.

Georgia inserted the battle flag into its state flag in 1956. Two years later, South Carolina made it a crime to desecrate the Confederate flag. And then, on the centennial of the day South Carolina opened fire on Fort Sumter came in 1961, it hoisted the battle flag above its Capitol.

It was a symbol of heritage—but that heritage was hateful. Two state delegations, in Charleston to mark that 1961 centennial, found themselves barred from the hotel where the ceremony was to take place because they included black members. President Kennedy had to issue an executive order moving the commemoration to the Charleston Navy Base. And when the centennial ended, the flag stayed, proclaiming that South Carolina might have lost the war, but that it was determined not to surrender its opposition to racial equality.

But the courage and sacrifices of the civil-rights movement dragged a reluctant nation forward. In 2000, following protests and boycotts, the flag came down from atop the dome, installed instead at a Confederate memorial on the grounds of the Capitol. Governor Nikki Haley now protests that her hands are tied by the legislation enacting that compromise, which dictates precisely how it must be displayed:

This flag must be flown on a flagpole located at a point on the south side of the Confederate Soldier Monument, centered on the monument, ten feet from the base of the monument at a height of thirty feet.

This history is not seriously contested. It has been documented in scholarly books, articles, and official reports. The flag was created by an army raised to kill in defense of slavery, revived by a movement that killed in defense of segregation, and now flaunted by a man who killed nine innocents in defense of white supremacy.

On Thursday, my colleague Ta-Nehisi Coates issued an unambiguous call: “Take down the Confederate flag—now.” Others have taken up his cry. But if it is no surprise to see the NAACP and other civil rights groups renew their consistent opposition, or to have the White House reiterate President Obama’s view that it “belongs in a museum,” opposition to the flag is spreading to new quarters, and growing stronger. “Take down the ‪#ConfederateFlag at the SC Capitol,” former Republican presidential nominee Mitt Romney tweeted on Saturday, renewing his opposition more clearly than ever before. “To many, it is a symbol of racial hatred. Remove it now to honor ‪#Charleston victims.”

Several Republican 2016 hopefuls also weighed in. Emphasizing that the decision is ultimately up to the people of the Palmetto State, Ohio Governor John Kasich added that, “If I were a citizen of South Carolina I'd be for taking it down.” Jeb Bush cited his own record of removing the flag from atop the Florida statehouse as a model. (Not all of their rivals concurred; some candidates for the highest office in the Union took a states-rights position on the battle flag of the Confederacy, apparently without irony.)

There are those who would still prefer to believe that the flag is the symbol of a purely noble cause and proud heritage, somehow twisted and perverted by the Dylann Roofs of the world. “It's him ... not the flag,” protested South Carolina Senator Lindsey Graham, who succeeded Strom Thurmond in the Senate.

But their numbers are shrinking. Russell Moore of the Southern Baptist Convention, a denomination birthed in defense of the rights of slaveholders in 1845, issued a remarkable plea:

The symbol was used to enslave the little brothers and sisters of Jesus, to bomb little girls in church buildings, to terrorize preachers of the gospel and their families with burning crosses on front lawns by night….The cross and the Confederate flag cannot co-exist without one setting the other on fire….Let’s take down that flag.

It will take a two-thirds majority in the South Carolina legislature to honor that call. But by Saturday evening, two Republican legislators had stepped forward to announce their support for such a move.

The South Carolina of Governor Nikki Haley and Charleston Mayor Joe Riley is no longer the South Carolina of Christopher Memminger and secession in defense of slavery. It is no longer the South Carolina of Strom Thurmond and massive resistance to desegregation. On this sesquicentennial of the dissolution of the Confederacy, the flag is a glaring anachronism, a rallying point for those who rage against progress they cannot halt. That is how it became the banner of Dylann Roof and terror in the name of white supremacy. So why does it still fly on the Capitol grounds?