I can tell you all exactly how all this has transpired and it is about 40 years in the making.
1976--Jimmy Carter won a tight election over Gerald Ford, but it was not really a surprise since Nixon had resigned in 1974 & Ford took over as the interim President. Carter was a party outsider who came as an outsider [much like Trump]. Carter's problem was that he did not have or know enough qualified people to make up his cabinet and join him in office. He hired far too many unqualified people. Most in the party truned against him, turned to Teddy 'Chappaquiddick' Kennedy who actually challenged a seated Pres for his own party's nomination. Carter spent so much effort in turning him back that he was a wounded duck, making way for Ronald Reagan. [plus the Iran Embassy hostage crisis and asking Amy about important issues and she said "control of nuclear arms"]
1980-88--Ronald Reagan--Ronnie knew enough from being in office to run on turning around a failing economy that was in Carter's high interest rate recession. He got his own budget & tax policies pushed thru Congress with ease, plus made great friends Tip O'Neill and also got friendly with Congress [something Obama refused to do from 2010-2016]
1988-1992-George H.W. Bush--rode Ronnie's coattails with a great economy and had it going. Had great approval ratings of over 70% after the 1st Gulf War, but forgot where he came from, got back to his far too moderate roots, made the quoted remarks "Read my Lips, no new taxes" and of course raised taxes, the economy started to tank as it is want to do in cycles and he got overtaken in 1992 by another like Jimmy Carter, a relative small-state unknown, Bill Clinton.
1992-2000--Bill Clinton rode the wave of the 1994 Newt Gingrich 'Contract with America' and the economy started going again. What the 1st Clinton didn't do though was vet and do background checks on people he put in his office [see Jimmy Carter]. Plus he tried to fast track Zoe Baird as his Attorney General and she was found to have an illegal immigrant housekeeper as a nanny, it was a scandal he couldn't live down the first 2 years. Cost him time. Many of his other employees were disloyal & unqualified. Clinton never stopped campaigning and his agenda was crappy--too many things with no focus and the Republicans exploited it. In 2 years they won back the House & Senate, Gingrich got The Contract, and the GOP is still riding a legacy today that has had 18 of 22 years in the House.
2000-2008--George Bush--had 9/11, rode the wave of massive support of America, but definitely lost focus when he altered the Afghanny plans of getting Bin Laden and all the real terrorists, starting into Iraq to go after Daddy's initial goal of getting Saddam Hussein, thus cost the U.S. trillions of extra $$$ and too many lives and he saw the U.S. debt over double from $5 T to $11 T. It cost the Republicans a few years of the House & Senate and more importantly led the country into the abyss known as "Obamacare"!
2008-2016--Barack Obama--Democrats squeezed out several recounts in Minnesota, Al Franken was finally given his oath of office in July 2009 and the Senate had their filibuster-proof 60th vote, thus unleashing the 2700 pages of an unread bill that Nancy Pelosi told us the House was supposed to vote first & read about later. A vote that later cost many Senators their jobs--Feingold, Specter, Lincoln, Nelson, Hagan, Landrieu, Begich, Pryor, Udall, Rockefeller, Baucus, Johnson, Harkin, Dorgan, Bayh, & Burris. Since losing his House & Senate in 2010, he did not do like Clinton did and get along with and work with Congress, choosing to stay arrogant and act like he did not need them. Making like it was the other party's fault. He and the Democrats paid dearly in 2016 and have now lost over 900 state house seats, governorships have flipped to 33 in favor of the Republicans, 247 to 188 in the House and 54 in the Senate. It could be years before this tidal wave is over as long as the Trump/Pence partnership holds strong and listens to Ryan/McConnell, his kids and the rest of his key advisors, picks more great cabinet members and keeps disregarding to the liberal know-nothing press.