According to former White House counter-terrorism advisor and ABC News consultant Richard Clarke, the business of pulling back on the massive security effort without a resolution to the bomb plot could be tricky business.

“They have to unwind the heavy security very slowly and in gradual steps — make it appear that some of the heavy security has gone away while actually keeping a lot of surveillance the public won’t see,” Clarke said.

In New York, police officials said they would maintain the tough security at least through the morning.

“The threat for me is fundamentally the same. It hasn’t changed. We don’t have really additional information to add,” NYPD commissioner Raymond Kelly told ABC News’ New York affiliate WABC Sunday, referring to the alleged bomb plot. “But there’s no reason to lessen our alert status.”