Executive privilege for Bannon?

The White House order not to speak essentially amounted to a gag order, Himes argued.

“This raises some very serious issues about whether we’ll get straight answers from anybody who is or was associated with the administration or is or was associated with the transition,” Himes said.

Himes confirmed that Bannon was subpoenaed during his more than 10 hour hearing to compel him to answer questions. However, Himes said, Bannon still asserted executive privilege.

[...]

Himes said he was not familiar with an individual using executive privilege as it relates to conversations with the president-elect, or conversations that don’t involve the president.

  The Hill

Perhaps because that privilege doesn't exist?

A source familiar with Bannon’s interview told The Daily Beast that despite the subpoena—issued by Devin Nunes, the typically Trump-friendly chairman of the committee—Bannon refused to answer questions about events that happened after Election Day.

[...]

“This was characterized as a result of his being there voluntary; he’s there of his own volition and could refuse to answer questions based on what the White House instructed him to do,” Schiff added. “We then were able to be promptly provide him with a subpoena and they went back to the White House and got the same instruction back again, basically: We don’t care whether it’s under compulsory process or voluntary basis, we’re instructing you to effectively put in place a gag rule.”

[...]

This situation has committee members concerned that other top White House officials will also refuse to answer their questions. Hope Hicks, the president’s communications director, is scheduled to testify before the committee this week.

  Daily Beast

I'm gonna go out on a limb here - she'll be under the same gag order.

Think about this for a minute: the White House has ordered people to ignore Congressional subpoenas. 

About things that happened before the president was the president.

...but hey, do what you want...you will anyway.