Upon leaving office Trump poses the single greatest threat to American national security that exists, based on the information he has, his reckless willingness to leverage it for personal gain, and the ways in which he is compromised to strategic adversaries. It would be shocking if natsec brass were not canvassing options for taking him out.
Their optimal window so as to minimise civil unrest would be after succession is formalised, but before transfer of power takes place, ensuring continuity but avoiding the incoming administration being perceived responsible. It is far more favourable if, as some predict, he resigns in anticipation of a pardon from Pence, at which point he becomes a civilian, thereby negating it constituting a coup, something they would be extremely averse to for all the right reasons.
It would be reckless in the extreme from the perspective of the natsec establishment to allow Trump to leave office and be a free man, and can be taken for granted that every adversarial intelligence agency has elaborate plans in place to pounce. There are too many reasons to count why Trump has targets painted all over him upon leaving office – painted by those who once served him, understanding the severity of the risks – and there’s plenty of precedent legitimising their concerns (e.g the CIA having to extract their most high-level Russian asset due to mishandling of information; and the Ukraine scandal). They’re completely aware of the prospect of Trump selling them out, and cashing in on PDBs for a billion bucks a pop.
It seems inevitable given the ubiquity of these anxieties, and the enormity of their implications, that there are plenty of capable players agitating to move.
 “Former CIA director George Tenet considered the PDB so sensitive that during July 2000 he indicated to the National Archives and Records Administration that none of them could be released for publication ‘no matter how old or historically significant it may be.’” – https://en.wikipedia.org/wiki/President's_Daily_Brief
 “Russia-US espionage: Details emerge of 'extracted spy'.” – https://www.bbc.com/news/world-us-canada-49651576
 “'It's Frightening All Around.' Former Intelligence Officials Warn Trump's Debt Is a National Security Threat” – https://time.com/5894199/trump-debt-national-security-threat/
 “Senate report details security risk posed by 2016 Trump campaign’s Russia contacts” – https://www.washingtonpost.com/national-security/senate-intelligence-trump-russia-report/2020/08/18/62a7573e-e093-11ea-b69b-64f7b0477ed4_story.html
 ”U.S. intelligence official told to halt Russian 2020 election meddling threat assessments: whistleblower” – https://www.reuters.com/article/us-usa-election-whistleblower-idUSKBN26032Q
 ”CIA clamps down on flow of Russia intelligence to White House” – https://www.politico.com/news/2020/09/23/cia-russia-intelligence-white-house-420351
 ”The Election That Could Break America” – https://www.theatlantic.com/magazine/archive/2020/11/what-if-trump-refuses-concede/616424/
 “Trump abused presidency for own gain, Democrats' impeachment report concludes” – https://www.theguardian.com/us-news/2019/dec/03/trump-impeachment-report-inquiry-house-democrats-findings-latest
 “Trump, Ukraine and Impeachment: The Inside Story of How We Got Here” – https://www.nytimes.com/2019/11/11/us/ukraine-trump.html