Wednesday night, a white man walked into a historically black church in Charleston, South Carolina, and shot nine parishioners. Today, a Confederate flag is flying on the grounds of the South Carolina statehouse in Columbia — as it does every day. While the flags on top of the statehouse itself are flying at half-mast, the Confederate flag (displayed at a Civil War memorial) is flying at full mast.

This is more than just an awkward juxtaposition. As Cornell historian Edward Baptist explains in a series of chilling tweets, the Confederate flag isn't just a symbol of the pro-slavery rebellion, it's also a symbol of post-Civil War white supremacy — including the KKK and other groups that expressed that supremacy violently, at times by attacking black churches. That it's flying today, after what Charleston police are describing as a hate crime, is profoundly ugly:

SC's stars and bars flag started as the battle flag of proslavery traitors who refused to accept an election's results. — Edward Baptist (@Ed_Baptist) June 18, 2015

In the course of Civil War, the flag became the symbol of not only slavery and treason, but the murder of black soldiers. — Edward Baptist (@Ed_Baptist) June 18, 2015

In the 1950s, the battle flag was revived not just as a symbol of resistance to federally mandated desegregation. — Edward Baptist (@Ed_Baptist) June 18, 2015

The stars and bars was also a symbol of terror: of the violent intimidation of African Americans who dared assert their rights. — Edward Baptist (@Ed_Baptist) June 18, 2015

The stars and bars promised lynching, police violence against protestors and others. And violence against churches. — Edward Baptist (@Ed_Baptist) June 18, 2015

SC's state flag is a flag of slavery. But it is also a flag of terrorism. — Edward Baptist (@Ed_Baptist) June 18, 2015

That terror is among other things anti-religious and particularly, anti-Christian.Churches have been bombed & burned for what it symbolizes. — Edward Baptist (@Ed_Baptist) June 18, 2015

Ministers, worshippers, people singing hymns have been attacked time and time again by those who serve it and those who wave it. — Edward Baptist (@Ed_Baptist) June 18, 2015

So here we are again.SC may lower the pro-terrorism, proslavery, anti-religious flag to half mast for a day.But they plan to raise it again. — Edward Baptist (@Ed_Baptist) June 18, 2015

The flag is still a live controversy in South Carolina. In October 2014, Governor Nikki Haley defended it as unproblematic for the state's business, saying, "I can honestly say I have not had one conversation with a single CEO about the Confederate flag."