Convinced of the painting’s power, Ms. Wicha helped raise $200,000 in private funds to buy it. She originally planned to unveil the painting in summer 2017, but decided to push the opening back a year after the election of President Trump. She didn’t want to create the impression that the museum had purchased the painting as some kind of protest. “It would be as if we had acquired it for a political statement, or the artist had painted it for a political statement,” Ms. Wicha explained.

The extra year also gave the museum time to engage the community. “I just felt that with a painting like this, the subject matter it’s taking on, the world we’re in, we needed to be really thoughtful in how we prepared,” Ms. Wicha said. “Would we have done this in a different political climate? I don’t know. But I can tell you that in this political climate it was the right thing to do.”

To provide that historical context, the Blanton hired six gallery “hosts,” at least one of whom will be in the gallery at all times (in addition to the security guard) to answer questions about the painting. A video screen in the gallery will play an interview with Mr. Valdez on loop. The wall text introducing the painting was written by the curator Veronica Roberts, who estimated that she had revised its six paragraphs at least 400 times. The exhibition will be complemented by a series of talks and programs beginning Tuesday and continuing through October, as well as an in-depth website.

Among all these efforts, however, the Blanton did not contact Nelson Linder, the local N.A.A.C.P. chapter president, until July 9.

“Something like this, not to call the N.A.A.C.P. is fairly ridiculous,” Mr. Linder said. “Out of courtesy, they should have let us take a look at it.”

After being made aware by this reporter of Mr. Linder’s concerns last week, Ms. Wicha invited the civil rights leader to view the painting and take part in one of the programs that will accompany the exhibition. Although Mr. Linder said he appreciated the museum’s finally contacting him, he expressed reservations about the painting itself. “I would have shown the victims,” he said. “Not just pictures of the Klan, but the end result of their behavior, the black folks being lynched.”