An entrenched uniparty rule with neoliberals and neoconservatives mostly in lockstep and every other ideology being merely performative. Remember Futurama aired in 1999 with the joke of John Jackson vs Jack Johnson criticizing each other's 3 cent titanium tax
There was always petty bickering and faux outrage and morality crusaders, politicians cynically riding cultural fads for their own gain. But having their positions made too secure within the uniparty created unhealthy uncompetitive conditions. If they don't need to listen to their voters, don't need to fight for their seats, don't need to adapt to popular causes it led them towards being more of the teapot dome era of fatcat aristocrats deciding the country's policies in smoke filled rooms. And of course, all the opportunities for blatant corruption. They could just get away with it, because they had each other's backs. You can see how Joe Biden was old enough to hail from that era, no need to compromise, no need to find common ground with opponents, no need to weigh the pros, cons and ethics of actions before taking them.
look to europe where you can have a dozen parties represented but they're all in lockstep on their EU agenda with a socialist state tempered by minor degrees of austerity, absolutely intolerant of any opposition. Its a pretty trite observation, but competitive forces are what evolve a society towards progress, while stale and idle societies become decadent and decayed