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Washington Post reporter Bob Woodward has shared with ABC News his email exchange with the White House official who told him he would "regret" his reporting on the sequester. That official was Gene Sperling, the director of President Obama's National Economic Council.

Woodward tells me that Sperling's words - "as a friend, I think you will regret staking out that claim" - was an implied threat because, Woodward says, the White House was not really disputing the facts.

"It's just not the way to operate," Woodward told me, saying Sperling's implied message was, "You challenge us, you will regret it."

Why did he respond to Sperling's email so politely? He was trying to keep open the lines of communication.

"They don't have to talk to anybody," Woodward said.