One party system? Yes, for many the matter is settled and T can do and want as he pleases.
But then, there are signs like Cramer dropping oil stocks, changes, however if for you the matter is settled, what can you do? Looks like a dead end to me.
During the Bush administration there was talk of a one party Republican system, but the Republican party is really closest to collapse. People like to tout that the two parties are both ill, but the Democrats have always battled with one another. It's kind of like the large Mediterranean culture family. They yell at each other over the dining table but in the end they mostly pull together. Democrats are a more fickle voting block though because they want to fall in love with their candidate and if they don't feel it, turn out will be lower.
The Republicans, especially since Reagan are a more hierarchical military sort of structure. There are times when people can express their wishes, such as during presidential primaries, but once the nominee is chosen, everyone is expected to fall in line behind the nominee even if that person is bad for the country, bad for the party, and a despicable human being. Because Republicans fall in line, they are more reliable voters.
There is some massive tension under the surface right now. Some Republicans have left the party and are organizing a resistance to Trumpism, and others are laying low and waiting for Trump to leave before they try to seize back the party while another group who were mostly the rubes the Republicans conned into voting for them over and over even though everything the Republicans did was not in their best interest. That group are rabidly pro-Trump and now that they got their guy, they will be looking for another Trump-like candidate when Trump is gone. That sets up a big fight for control of the party and when Republicans fight each other, they mean it. It's not just a dinner table spat.
This difference was illustrated last year when Occassio-Cortez and Pelosi were tussling a bit. The Republicans saw it as strife in the party and Trump was stupid enough to try and frive a wedge in the party. He utterly failed because he didn't understand the dynamic of the Democratic party. Pelosi told Trump to butt out of the family argument and things settled down between her and AOC.
Demographics are also coming into play. Every year the US voting public becomes about 1/2% less white. The share of the white vote drops about 2% every election cycle. It was believed that 2012 was the last time a Republican could win by appealing mostly to white voters, but Trump temporarily reversed the trend and the white percentage of the vote in 2016 was just about equal to 2012. Minorities did not turn out as well and Trump got some white voters who had given up voting to vote for him.
The 2018 midterms reverted to the norm and while the midterm turnout is always more white than presidential elections, the percentage of the white vote from 2014 to 2018 dropped by about 2%. If that trend continues this year, the percentage of white vote will drop about 4% off of 2012 and 2016 numbers. That spells doom for Republicans who are a predominantly white party.
There is a movement by people like Bill Barr to turn the US into a white dictatorship before it becomes impossible for a Republican (of the party as it's constituted now) to win the presidency again.
In the next decade if the US goes through a period of being de-facto one party state and the Constitution holds, it will be a Democratic dominated government. The out of power party always regroups and comes back, or another party comes back in its place (as happened in the 1850s when the Whigg party fell apart and the new Republican party sprang up). Party systems usually last 30-50 years. The New Deal party system lasted from 1932 to 1980 and the Reagan party system has lasted from 1980 to now. At the end of party systems there is usually a feeling that the old ways don't work anymore and things are falling apart. The 70s were a chaotic time with the country coming to terms with the Vietnam War, the economic chaos from the US losing direct control of the world's oil market, and political fallout from Watergate.
The 20s ended with a massive Depression. Another party system ended with the start of the US Civil War.
The last president of an old party system is always, with one exception, the "in power" party for the last decades, and he is always a one term president who is seen as a failure. The incoming president has new ideas and a new direction. That would argue in favor of Bernie Sanders. But Trump is so chaotic people might run for the safe harbor of Biden only to have him have to step down for health reasons or die in office leaving his VP to take the country in the new direction.
That is a similar scenario to the one time one party ran the country through two party systems. In the 1900 presidential election popular rabble-rouser Teddy Roosevelt was picked for VP to shut him up. When McKinley was assassinated, Roosevelt took over and started the party system that ran until 1932.
The "out" party does win the presidency during a party system, but the out party takes on the memes of the in control party. Thus Democrats have talked in terms of trickle down economics over the last 30 years and both Eisenhower and Nixon were very liberal compared to Republicans post Reagan.