Why does Atticus say Tom Robinson won't be safe if he is moved?

Atticus believes that if Tom is moved he will be in danger. As long as he's in the Maycomb jail, Atticus can protect him.

“…movin‘ him to the county jail tomorrow,” Mr. Tate was saying, “I don’t look for any trouble, but I can’t guarantee there won’t be any…”
“Don’t be foolish, Heck,” Atticus said. “This is Maycomb.”
“…said I was just uneasy.”
“Heck, we’ve gotten one postponement of this case just to make sure there’s nothing to be uneasy about. This is Saturday,” Atticus said. “Trial’ll probably be Monday. You can keep him one night, can’t you? I don’t think anybody in Maycomb’ll begrudge me a client, with times this hard.”