Read: Intelligence watchdog's letters about "urgent" whistleblower complaint

• In a letter dated Sept. 9, Atkinson stated that the complaint — which he found credible — consists of a "serious or flagrant problem, abuse or violation of the law" that involves classified information, but "does not include differences of opinion concerning public policy matters."
• In a second letter dated Sept. 17, Atkinson expressed dismay at the acting DNI and the Justice Department's decision to withhold the whistleblower complaint from Congress because they believed it does not concern an intelligence activity within the DNI's authority. Atkinson countered:

"I set forth the reasons for my concluding that the subject matter involved in the Complainant's disclosure not only falls within the DNI's jurisdiction, but relates to one of the most significant and important of the DNI's responsibilities to the American people."

Read the letters:

Go deeper ... Schiff: DNI's refusal to turn over whistleblower complaint is "unprecedented"

• "After nearly a month of stonewalling, it appears clear that the President has chosen the path of defiance, obstruction, and cover-up," the letter reads.

The state of play: Several White House officials have told Axios' Alayna Treene that the administration has no plans of complying with the committees' demands for interviews or documents without a full House vote formally approving an impeachment inquiry.

The big picture: The Trump administration's initial refusal to turn over the whistleblower complaint on the president's interactions with Ukraine is what led House Speaker Nancy Pelosi to finally support a formal impeachment inquiry.

Go deeper: Trump letter dares Pelosi to hold vote on impeachment inquiry

• Johnson asked the Justice Department earlier this week to look into links between Ukraine and Hillary Clinton's 2016 presidential campaign. His letter questioned the narrative that Biden's actions in Ukraine had nothing to do with his son's connection.
• However, it was also discovered that he signed onto a 2016 letter that mirrored Biden's work to reform Ukraine's prosecutor general and judiciary.
• There is no evidence that Biden's reform work in Ukraine was to protect his son's business dealings, as the president and some of his allies allege, or that he committed any form of corruption.

The state of play: Sondland, a Trump political appointee who donated $1 million to the president's inaugural committee, denied that there was a quid pro quo between the Trump administration and Ukraine's government in a series of text messages that former Ukraine special envoy Kurt Volker provided to a group of House committees investigating the Trump-Ukraine matter.

• "I think it’s crazy to withhold security assistance for help with a political campaign," Bill Taylor, the top U.S. diplomat to Ukraine, texted Sondland.
• Sondland texted back: "Bill, I believe you are incorrect about President Trump's intentions. The President has been crystal clear no quid pro quo's of any kind."
• The New York Times reported that Sondland's response came only after he spoke to the president.

Go deeper: House committees release texts from former Ukraine envoy Kurt Volker