A source familiar with discussions inside President Trump’s impeachment team says Ambassador Gordon Sondland not appearing is “part of an overall strategy connected to what is viewed as irregularities in the House impeachment inquiry.”

“The days of playing nice are done,” the source said.

Some context: The contrast with how the White House dealt with Special Counsel Robert Mueller is notable. John Dowd, Trump's former lawyer, once noted Mueller was part of the executive — but Congress is outside and the White House and Trump do not feel an obligation to be as cooperative.

A letter to House Speaker Nancy Pelosi addressing White House concerns is expected this afternoon. The letter is “still being massaged,” the source said, but it is expected to indicate the White House strategy moving forward.