House Democratic Leader Nancy Pelosi Nancy PelosiPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare House lawmakers reach deal to avert shutdown Centrist Democrats 'strongly considering' discharge petition on GOP PPP bill MORE (Calif.) on Thursday called President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE’s furious reaction to an anonymous administration official's op-ed disparaging him in The New York Times a “manifestation of his instability.”

Pelosi said her “first thought” was that Vice President Pence penned the opinion piece, which described efforts among staffers in the Trump administration to push back against the president's worst instincts.

Not long after the op-ed was published Wednesday afternoon, Trump tweeted, “TREASON?” He later demanded the Times identify the piece's author "for National Security purposes."

House Minority Leader Nancy Pelosi says Pres. Trump referring to the anonymous New York Times op-ed as "treason" is "a manifestation of his instability" https://t.co/vsAvY1h5A6 pic.twitter.com/yLE77tvbdg — ABC News Politics (@ABCPolitics) September 6, 2018

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“The president saying it’s treason is, again, a manifestation of his instability,” Pelosi said. “But what was said in there is a reflection of what we hear from many Republicans around the country, not in Congress: That the party of Lincoln cannot survive as the party of Trump.”

Pelosi added that it “probably won’t take too long for us to find out who wrote it.”

“Who has denied it already? The vice president,” she said. “That was my first thought.”

Jarrod Agen, Pence's deputy chief of staff and communications director, on Thursday denied that Pence authored the op-ed, tweeting that the vice president's office "is above such amateur acts."

Several other White House officials have also denied writing the op-ed, including Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenDHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections Democrats smell blood with new DHS whistleblower complaint MORE, Secretary of State Mike Pompeo Michael (Mike) Richard PompeoOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Overnight Defense: House Democrats unveil stopgap spending measure to GOP opposition | Bill includes .6B for new subs | Trump issues Iran sanctions after world shrugs at US action at UN Navalny calls on Russia to return clothes he was wearing when he fell ill MORE, Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE, Treasury Secretary Steven Mnuchin Steven Terner MnuchinOn The Money: Powell, Mnuchin stress limits of emergency loans | House seeks to salvage vote on spending bill | Economists tell lawmakers: Kill the virus to heal the economy Economists spanning spectrum say recovery depends on containing virus Powell, Mnuchin stress limits of current emergency lending programs MORE, Interior Secretary Ryan Zinke Ryan Keith ZinkeTrump extends Florida offshore drilling pause, expands it to Georgia, South Carolina Conspicuous by their absence from the Republican Convention Trump flails as audience dwindles and ratings plummet MORE and Director of National Intelligence Dan Coats Daniel (Dan) Ray CoatsFBI chief says Russia is trying to interfere in election to undermine Biden The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Former Intel chief had 'deep suspicions' that Putin 'had something on Trump': book MORE.

The anonymous Trump official in the op-ed bashed the president's "amorality" and praised the work of "unsung heroes" who push back against him, suggesting a coordinated effort from within.