All you have to do to defeat that is to fucking vote. Bernie lost the Presidential primaries in 2016 ans 2020 because more people voted for Clinton and Biden.

Yeah, there was talk about them rigging the 2016 primary for Clinton with the superdelegates if Bernie was ahead, but it never reached that point because Clinton secured the nomination before the convention.

I teach at a university and I had a ton of students praising Bernie who couldn't be assed to change their registration to a local address or drive home for a day to vote for him. And then they refused to vote in the general because they were protesting that the person they couldn't be bothered to vote for didn't win the nomination.

I would phrase it as:

Each party sends a candidate to compete in the general election. The primary elections are the party's internal elections to decide who their candidate is.

In the United States, elections for the office of the Presidency are held every four years. Fun fact: the first few elections, the winner of the race got to be the president, and the runner up was made the vice president. The great experiment in democracy yielded data: That doesn't fucking work! So the candidates for vice president are selected by the presidential candidates during the campaign cycle. As a major job of the president is to appoint people, this is the free sample you get. They then run as a pair, the vice presidential candidates are often called "running mates." These get a lot of attention, you'll hear these called Major Elections. The next one is still tentatively scheduled for 2028.

Congress...is kinda fucking stupid. But also, the term "congressman" refers strictly to members of the House of Representatives; members of the upper house are addressed as "senator." Congressmen serve 2 year terms with no term limits. We re-elect the entire lower house every 2 years, almost to a man. Half of those elections line up with a presidential election, the ones that don't are often called "Midterm elections." There is a mid-term this year.

The Senate is even weirder, senators serve 6 year terms, and every two years a third of the senate is up for re-election. From an individual state's perspective, that means one of your senators is up during one election, the other one is up two years later, and then neither is up two years after that. Because 100 isn't divisible by 3, there's an exception to that somewhere, I'm not sure where it is off the top of my head.

It gets a little complicated because each party, the Democrats, Republicans, and The United Collective Of Parties That Are Allowed To Exist Because Of The First Amendment Assembly Clause But Not Allowed To Matter, and each state, are allowed to choose how their primaries (and their elections) work.

In many states, such as my home state of North Carolina, a primary election looks like the main election, The party issues a paper ballot, you bubble with a pen and insert into the box. Other states have "caucuses" where you go to a big room and vote by physically sitting in the area designated for the candidate you support. Some parties in some states welcome anyone to participate, some allow only registered members of that party to participate. Such is life in a federation.

Most, I think all, states also line up their own elections with the Federal elections. So every two years you walk into the polls for a 1/2 chance of voting for a President and vice president, 2/3 chance of voting for 1 senator, 1 congressman, quite possibly a governor, lieutenant governor, general assemblyman, state senator, county commissioner, sheriff, district judge, town mayor, 3-7 school board members, dog catcher and village idiot.