Donald Trump continues to argue that the Republican presidential-selection process is “rigged" and that any result other than his getting the party's nomination would be an affront to democracy. The response that "Trump knew the rules" is true but isn't the strongest rebuttal to his claim. The more compelling argument is that those rules require some candidate to get majority support, in some form, but Trump is disdainful of the principle of majority rule.
If Trump gets a majority of the 2,472 delegates before the convention, he will become the nominee. Otherwise, the candidates, none of whom are likely to be the private favorite of a majority of the 2,472 delegates, will all have to try to convince a majority of them that they are the best option. In the end, one candidate will convince a majority of that very thing. Trump just doesn't like his chances of being the candidate to do so, not so much because the delegates aren't representative of the voters, but because they are: Most Republican voters don't want Trump to be the nominee.
Indeed, the only reason Trump will be close to a majority on the first ballot is because the system has rewarded him with a far higher percentage of delegates (49 percent of those awarded to date) than his percentage of votes (38 percent).
To date, 62 percent of voters in the Republican presidential race have voted against Trump. Not only did that 62 percent not back Trump, but many—perhaps most—wouldn't have included him among their top two, three, or even five candidates. In this light, the notion that he is somehow owed the nomination seems a bit ludicrous.
James Madison called majority rule the "first principle of free government." Abraham Lincoln said that "rejecting the majority principle" results in "anarchy or despotism."
At its core, Trump's position is an assault on majority rule. He is arguing that a majority (of delegates) should be bound by a plurality (of voters). But what was good enough for Madison and Lincoln should be good enough for Trump.