Didn’t help it was freezing and the o-rings couldn’t take cold.
From Wikipedia [Columbia accident], which agrees with other reports I studied:
What the Rogers Commission report did not highlight was that the vehicle was never certified to operate in temperatures that low (below freezing). The O-rings, as well as many other critical components, had no test data to support any expectation of a successful launch in such conditions. Bob Ebeling from Thiokol delivered a biting analysis: “[W]e’re only qualified to 40 degrees ...’what business does anyone even have thinking about 18 degrees, we’re in no man’s land.’”[2] Ken Iliff, a former NASA Chief Scientist who had worked the Space Shuttle Program since its first mission (and the X-15 program before that) stated in an official 2004 NASA publication, “Violating a couple of mission rules was the primary cause of the Challenger accident.”[3]
We saw icicles on the pad cctv feeds that morning. A lot of us thought they would scrub the launch.