Did Chris Christie Try to Stop BridgeGate Investigation

Daily Kos posted this piece from the Wall Street Journal (paid subscription) about how Gov. Chris Christie called New York Gov. Andrew Cuomo on the week of December 12. The date is very important. Christie said in his press conference that he only found out his staffers plotted to close the lanes to the day before.

Mr. Christie, a Republican, complained in a private phone call to Mr. Cuomo, a Democrat, that Patrick Foye, the executive director of the Port Authority of New York and New Jersey, was pressing too hard to get to the bottom of why the number of toll lanes onto the bridge from Fort Lee, N.J. was cut from three to one in early September, according to this person. The lane closures occurred without notice to local authorities, officials have said, and snarled traffic for a week in the small borough on the Hudson River bluffs.

The question is if Christie didn't know that his staffers were plotting to create a traffic jam then why did he call Cuomo to get Foye to back off on his investigation?