DETROIT – Here’s something that virtually everybody assumes about next year’s presidential election — but which may not be true:

          We will know who the Democratic presidential nominee will be long before their party’s convention opens in Milwaukee July 13.

          If recent history is any guide, we will.

           But we very well might not. The conventional thinking goes like this: Sure, there is still a virtual forest of candidates for the Democratic nomination — 19 as I write this — something that may well be true for the rest of this year.

But then, like a Japanese sumo wrestling match, things should be settled fairly quickly. The Iowa caucuses happen Feb. 3; the New Hampshire primary eight days later.  Any candidates who don’t make a credible showing in either will see their funds dry up.

South Carolina votes on Saturday, Feb. 29, and any of the African-American candidates who don’t score well with that largely black electorate should be toast.

Four days later, after an avalanche of 14 states vote on March 3, the so-called “Super Tuesday,” there may be no more than two or three candidates left. The whole thing may be settled the next week, March 10, when Michigan and five other states vote.

By the time Ohio and Illinois hold their primaries March 17, two-thirds of the states will have voted, and it all should be over.

That’s pretty much how it has gone, with a few variations, since 1952. People often forget that the primaries and caucuses are held to determine who gets how many delegates to the national convention.

Nor do many voters know that the convention is where the nominee will be actually selected, and that whoever it is will need a majority of the delegates, not just more than anyone else.

 What if Joe Biden hangs in there as front-runner, but is unable to win anything like a majority of the 3,769 delegates chosen by the voters? What if he wins 1,100, say – but Elizabeth Warren gets 900, and Bernie Sanders and Kamala Harris each get 700 or so, and a smattering of other candidates get the remainder?

  If that happened, and no one dropped out – we would see a spectacle that hasn’t taken place in nearly a lifetime.

The roll of the states will be called on Wednesday night, July 16.  The total will be announced, the clerk will proclaim that no one had a majority, and that they would, maybe after a brief recess, vote again.

And maybe, just maybe … again and again and again.

Things would, indeed, get wild and crazy if nobody were to go to the Democratic convention with a majority. For starters, if that’s the case the 765 so-called “super delegates,” mainly elected officials, would not be able to vote on the first ballot.

Their powers were diminished after heavy criticism that they unfairly tilted the process in the past, especially in favor of Hillary Clinton last time. But they could tip the balance after that first vote.

On top of that, delegates won by a candidate in the primaries — Bernie Sanders, say — would no longer be bound to that candidate after one or at most two ballots. After that, anything goes.

They could vote for anyone – including people who weren’t even candidates. Could a deadlocked Democratic convention turn to someone like Al Gore, say?  Possibly yes –though that’s unlikely.

What would almost certainly happen if no one had a majority on the first ballot would be deal-making behind the scenes, in which offers would be made by some candidates to get others to drop out.

Offers like the vice-presidency, say, or a pledge that the winner would take certain positions on, say, health care or the environment.

 That is how things worked in both parties for over a century.  It took Abraham Lincoln three ballots to be nominated in 1860, and Franklin D. Roosevelt four, in 1932.

But that was when the power was held mainly by party bosses, who often really did select candidates in smoke-filled rooms.

Sometimes, however, that system broke down.

The ultimate nightmare scenario took place in 1924, when Democrats were deadlocked between two factions, and voting went on for more than two weeks before the main candidates withdrew, and an obscure lawyer named John Davis won what had become a totally worthless nomination on the 103rd ballot.

That spooked everyone.  Adlai Stevenson was the last candidate not to be nominated on a single ballot.

Yet it could happen again.  For example, the rules have changed for Michigan’s Democratic primary next year, and the complex selection process they’ve adopted may well scatter their votes.

The state will have 147 delegates in Milwaukee, 125 of them to be selected in the primary. But they will be distributed by a complex process in which 98 will be elected by congressional district, and another 27 statewide, under a proportional system.

Some congressional districts will have four delegates; some nine. Any candidate will have to have 15 percent to get any. The people who will serve as delegates themselves won’t even be chosen till May and June, and then they will be joined by 22 super delegates.

Good luck figuring all that out.

Republicans, meanwhile, have a much simpler process. Their primary will be held the same day, and any candidate has to have at least a fifth of the vote to get any delegates.

If anyone gets more than 50 percent, they get all the delegates, under new rules clearly designed to benefit President Trump.

There are still more than four months to go, and nobody really knows yet how this will all turn out.

But it just might be even crazier than you ever dreamed.