What's new: "60 Minutes" first reported that the whistleblower was under federal protection because of safety fears. But the whistleblower's lawyer Mark Zaid tweeted that the show "completely misinterpreted" the contents of the letter.

"Nor have we ... reached any agreement with Congress on contact with the whistleblower. Discussions remain ongoing."

— Lawyer Mark Zaid's tweet

However, Politico's Natasha Bertrand notes, the letter does state, "[W]e appreciate your office’s support thus far to activate appropriate resources to ensure their safety."

The big picture: Trump and his associates have doubled down in recent days against allegations that he may have pressured Ukrainian President Volodymyr Zelensky to investigate 2020 candidate Joe Biden and his son Hunter Biden, as House Democrats step up their formal impeachment inquiry.

The president continued his days-long attacks on the whistleblower and House Democrats Sunday, declaring "I deserve to meet my accuser" and accusing House Intelligence Chairman Adam Schiff of treason.

What they're saying: Schiff said to "60 Minutes" in its special report on House Democrats' impeachment inquiry of Trump's demand to know who reported his call to Zelensky, "It’s hard to describe how dangerous and loathsome that invitation to violence is."

House Speaker Nancy Pelosi told CBS journalist Scott Pelley that Trump phoned her early last week to say "there was nothing wrong" his conversation with Zelensky as calls for his impeachment grew among Democrats.

"It is wrong for a president to say that he wants you — another head of state — to create something negative about his possible political opponent to his own advantage, at the expense of our national security, his oath of office to the Constitution and the integrity of our elections."

— House Speaker Nancy Pelosi's comments to "60 Minutes"

House Minority Leader Kevin McCarthy told "60 Minutes," "The president did nothing in this phone call that's impeachable."

Read the letters from the whistleblower's lawyer:

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Editor's note: This article has been updated with new details throughout.