Shortly after he lost a commission on the Cosmo-Slotnick Building, sculpture Steven Mallory took a shot at Ellsworth Toohey as he was getting out of his car to deliver a radio address (which missed by an inch). Ellsworth Toohey took it very calmly, giving the address exactly as planned.
After finding out about the news, Peter Keating was initially worried about whether the newspaper would still be publishing Ellsworth Toohey's column the next day, which was to speak very flatteringly of him. Once he realized that Toohey wasn't dead, though, his reaction changed (especially upon learning the identity of the assailant):
Keating stared - his throat dry - at the name of the assailant. It was Steven Mallory.
Only the inexplicable frightened Keating, particularly when the inexplicable lay, not in tangible facts, but in that causeless feeling of dread within him. There was nothing to concern him directly in what had happened, except his wish that it had been someone else, anyone but Steven Mallory; and that he didn't know why he should wish this.
When Toohey found out who it was:
When he heard the name, Toohey's glance remained fixed somewhere between the shoulder of one man and the hat brim of another. Then Toohey - who had stood calmly while a bullet struck an inch from his face against the glass of the entrance door below - uttered one word and the word seemed to fall at his feet, heavy with fear: "Why?"
Mallory himself indicated that him and Toohey had never met in person, he knew none of Toohey's friends, and that he didn't think that Toohey had anything to do with him losing the commission (which was perfectly true). The main connection was that Toohey had criticized him in his column at one point.
That being the case, why were Toohey and Keating so frightened by the Mallory's action?