Let's say that Donald Trump doesn't get the 1,237 delegates he needs in order to clinch the nomination before the Republican convention this July. Let's say, just to pick a number, that he gets 1,234. He walks into Cleveland at the front of an army of 1,234 people, all of whom will vote for him on the first ballot of the Republican nomination contest.

That's bad news for Donald Trump.

The problem for Trump is that if he doesn't hit that 1,237 number, all bets are off. Once he walks into the doors of the convention, he has those 1,234 delegates for one vote. After that one vote, if he doesn't have a majority, a subset of those delegates get to vote for someone else, if they want. And as we noted last week, Ted Cruz's campaign is doing its best to make sure that the people who make up Trump's delegate total want to vote for Cruz, not Trump, as the voting progresses.

But come on, you might be thinking. Clearly, if Trump is that close to a majority, he'll end up taking it, right?

And the answer is: Not if history is any guide.

Using CQ's Guide to U.S. Elections, we looked up every convention in which no one had a majority on the first vote since 1872. And in the majority of those, the person who had the most votes on the first ballot did not end up as the party's nominee.

In each of the contests labeled in yellow below, the leader at the outset (represented by lighter colored bars) ended up losing.

1876, James Blaine led on the first vote, lost to Rutherford B. Hayes.

1880, Ulysses Grant led on the first vote, lost to James Garfield.

1888, John Sherman led on the first ballot, lost to Benjamin Harrison.

And so on.

All of these are separate elections with separate dynamics. The Democratic convention of 1924, for example, was a year's worth of drama packed into over two weeks of voting. That doesn't tell us much about what will happen this year (though, again that year, the first-ballot leader didn't win). What it should remind us, though, is that the convention is not an election. It is an extended argument with flexible rules and no shortage of arm-twisting.

It's worth noting that all of these contests happened at a time when the link between primary voting and the nomination was much weaker -- at a time when the front-runner couldn't summon up mass indignation by tweeting about how he'd been wronged. In other words, Trump introduces a new dynamic that wasn't present in the past: public pressure.

Will that change things? If Trump gets 1,237 delegates, we'll never know.

If he doesn't? Buckle up.