Here's an outstanding article from The Atlantic that describes precisely why the Trumpian attempts at manipulating intelligence - from the CIA, DIA, FBI, and other such sources, not Ol' Heel Spurs' own rather dubious smarts - are extremely dangerous.
The high cost of politicizing intelligence
The article dovetails very nicely with works that examine in varying detail how well that worked for other administrations. McMaster's "Dereliction of Duty" (outstanding read, BTW, readily available from Amazon); Ricks' "Fiasco: The American Military Adventure in Iraq, 2003 to 2005;" Sheehan's "A Bright Shining Lie;" Halberstam's "The Best and the Brightest;" Shawcross' "Sideshow: Kissinger, Nixon,and the Destruction of Cambodia;" Prochanu's "Once Upon a Distant War"... a series of testimonials to the death and misery caused by presidents and their sycophants when they politicize the intelligence agencies.
But what the hey ... it keeps the national cemeteries filled up, and gives the flag-wavin' super-patriots something to do on Veterans' Day. And it creates jobs! All those illegal workers, pumping out Gold Stars for windows across America ...