I almost want to argue that Tom Clancy wasn’t all that good to begin with. His first books were collaborations with Larry Bond (who is an accomplished techno-thriller writer in his own right) and it seems clear that Bond did a lot of the heavy lifting, particularly in Red Storm Rising. As the series goes on, the stories just get stranger and stranger. Spoilers for the Clancyverse, which I am not going to code since the books are legitimately old now.
Patriot Games: Jack Ryan comes to the rescue of Charles and Diana and fights off vicious IRA terrorists who manage to outwit the Secret Service.
The Cardinal of the Kremlin: in a truly byzantine plot, Jack Ryan manages to talk the head of the KGB into defecting. There’s also a plot with a Russian agent who has a breakdown because she is a lesbian and can’t keep herself together around a nerdy guy’s hot wife.
Clear and Present Danger: America is going to win the drug war by kicking ass! This was probably Clancy’s best solo effort but it is also a very odd fantasy about how the drug war should be fought: fighter jets shooting down drug planes and commandos killing Columbian drug peons.
The Sum of All Fears: Clancy drops all pretense of reality so we can have a brink of WWIII plot. Palestinian terrorists find and rebuild a nuke, a Russian sub captain tracks and destroys a boomer, a “Peace Bowl” at the Vatican solves the Palestinian issue by having the Swiss Guards provide security and the nuke goes off at the SuperBowl in a massive blast of contrivance that convinces the US that it was a huge Russian nuke so that the President can go nuts overreacting.
Without Remorse: A Navy SEAL goes on a revenge fantasy mission after drug dealers kill the redeemed prostitute he was falling in love with. He also single-handedly invades Vietnam and captures an important Russian while killing the evil Viet Cong who was torturing American soldiers. Let us not forget a corrupt cop who somehow happens to be everywhere at once and a brilliantly-staged fake death that allows John Kelly to become the nefarious Mr. Clark.
Debt of Honor: well, since Russia decided to make peace and stop being an Evil Empire, it would seem we need a new enemy. Who has lots of money and technology? Japan! That’s right, let’s not forget who was running an evil empire before it was cool! And they’re going to torpedo both the financial markets and the remaining two aircraft carriers in the Pacific at the same time because there’s nothing the Japs (Tom Clancy’s term, not mine!) love more than fucking Americans! And they’re so damn serious about kicking America’s ass that they’re going to build themselves some nukes too! But fear not, America can recover from the financial crisis by pretending it never happened! The nukes are easily found and destroyed and the aircraft carriers are repaired in time for a big battle scene near the end. This novel is mostly remembered for the prescient scene of an airliner slamming into a building at high speed in a suicide attack. Other than that, it’s pure political fantasy.
Executive Orders: what if we had a president who didn’t have a congress, senate, supreme court or anything else to answer to? If DoH was political fantasy, this is political fantasy on speed and coke and a dozen Red Bulls. Iran and Iraq combine to form one huge Islamic Republic and they start crusading across the deserts of Saudi Arabia after attacking America with the ebola virus. However, two brave brigades stand in the way of the UIR’s impressive army and they prevail through luck, pluck and superior technology in addition to their in-depth knowledge of the Civil War. The bad guy is killed on live TV courtesy of the Ryan Doctrine.
Rainbow Six: enviro-terrorists weaponize ebola even further and plan to release it at the Olympics but the brave multinational Rainbow team defeats them!
The Bear and the Dragon: the dirty little Communist Klingon child-molesting baby killing godless heathen Chink cocksuckers (all terms used repeatedly in the book) sometimes known as the Chinese have decided to invade Siberia for massive oil and gold reserves. America defeats them in three shots- an artillery barrage, an airstrike and the timely use of “magical pigs”. China tries to nuke Washington DC but a single brave Aegis ship (with President Jack Ryan on the bridge no less) shoots the nuke down just in the nick of time. I don’t know if Tom Clancy just had some really bad Chinese food when he wrote this book but not only is it way over the top ridiculous it is also horribly racist, with every single American character busting out a colorful variety of epithets every single time the Chinese are mentioned.
Red Rabbit: Tom Clancy wipes his ass and sells the result. Oh, and Jack Ryan, before he was anybody special, personally saves the Pope from assassination.
The Teeth of the Tiger: Arab terrorists are back in style post 9-11 (which happened in the Clancyverse but is never contrasted with the even more horrible events such as a nuke going off the heart of an American city) and America has a new super-secret spy agency that can kill terrorists using special pens filled with heart-attack inducing poison. Just in time too because Al Qaida has teamed up with the Colombian Cartel for a double dose of terrorist badassery!
So as you can see Tom Clancy didn’t really go from strength to crap. More like his crap gained strength.
I should also mention Anne Rice, whose early novels were compelling but whose later efforts just became a showcase for her immortal, unkillable, beloved vampires who were evil but really felt bad about it.