Democrats demanded that Whitaker recuse himself from Special Counsel Robert Mueller's Russian Federation investigation. The news added yet another layer to previous reports that the president once speculated about why "my guys" at the "Trump Justice Department" weren't doing more to shield him from Mueller's scrutiny.
And no, it was not the top story of the day, because, in the morning, President Donald Trump had fired his Attorney General Jeff Sessions, the CBS late-night host revealed, which seemed to come as news to many in his Ed Sullivan Theater audience, based on their reaction.
The departure of Mr Sessions, who was the first USA senator to back Mr Trump's presidential run in 2016, was long expected, and came one day after Republicans lost control of the House of Representatives but boosted their Senate majority.
Sessions' chief of staff, Matthew Whitaker, has been appointed as acting attorney general.
Senator Susan Collins said: "It is imperative that the Administration not impede the Mueller investigation".
Whitaker is expected to oversee the investigation despite being critical of it in public statements and chairing the campaign of a witness in the probe.
Moreover, The New York Times reported earlier this year that Trump once ordered the White House counsel Don McGahn to stop Sessions from recusing himself, and that when McGahn was unsuccessful, Trump erupted in anger, saying he needed Sessions to "protect" and "safeguard" him.
With the midterms over, Special Counsel Robert Mueller is believed to be preparing fresh indictments against Trump campaign figures, possibly including his son Donald Trump Jr. and a former campaign consultant Roger Stone, and could press for the president himself to answer questions. Democrats had promised to reopen the House Intelligence Committee's investigation into Trump, to investigate Trump's finances, and to obtain his tax returns.
Dean said the firing of Sessions was "planned like a murder".
The relentless attacks on Sessions came even though the Alabama Republican was the first US senator to endorse Trump and despite the fact that his crime-fighting agenda and priorities - particularly his hawkish immigration enforcement policies - largely mirrored the president's.
Nadler says he wants to know why Trump is making the change and "who has authority over Special Counsel Mueller's investigation?"
Mr Trump had made his unhappiness publicly known, griping that he would not have picked Mr Sessions for the post, had he known the Attorney-General would step aside to allow the "witch hunt" to go on.
Mr Whitaker is considered by some as partisan at best and a Trump loyalist at worst.
But the relationship was irreparably damaged in March 2017 when Sessions, acknowledging previously undisclosed meetings with the Russian ambassador and citing his work as a campaign aide, recused himself from the Russia investigation.