What exactly is the deep state, and how much of a threat is it to President Trump?

For context, this is a question I answered on Quora

The deep state is exactly the part of the government that does not face democratic scrutiny and oversight and is entirely controlled by an entrenched bureaucracy that is accountable only to industries that stand to profit from their actions. Aside from the CIA, DHS is arguably the second most deep statist agency in the federal government, especially certain sub-agencies such as CISA which was ostensibly created by the first Trump Admin in 2018 to ‘counter foreign election influence’ but mission creeped their way into policing “misinformation” and “malinformation” on social media, which they vaguely defined as any information that undermined government authority and objectives, in the span of two years. No one voted for the Virality project that CISA coordinated with the Standford Internet Observatory and other unelected NGO “disinformation” think tanks. While the Obama Admin got the ball rolling on turning the DHS towards thought policing through the 2016 Countering Foreign Propaganda and Disinformation Act, which was Trojan horsed through the 2017 NDAA and established the first iteration of thought police with the Center for Information Analysis and Response, it is Trump who continued the process by adding CISA in 2018 and in his second Admin, using another DHS subagency to go after anti-war protestors who are permanent residents and student visa holders. The setup of DHS fusion centers are very similar to the provincial reconnaissance units the CIA set up during Operation Phoenix to fight an ideological war with dragnet surveillance of the populace and extrajudicial punishment of people deemed to be ideological threats such as putting them on blacklists that prevent them from flying or subject them to extra searches at the airport or that lead local police to . This is exactly the part of government that Trump has given more power to attack his ideological enemies for actions as innocuous as co-writing a student editorial critical of a University’s investments in Israeli companies, a year before Trump even took office. And when the Democrats regain the Oval office they will once again give more power to DHS to attack their ideological enemies. Taping Palantir, a private sector CIA cut out literally start with In-Q-Tel seed money to sell data mining and analytics software to the CIA, to continue the Total Information Awareness objective of the Bush Admin via centralized database with every data point the government has on all citizens is not fighting the deep state: he is enabling it.