This one number explains Donald Trump's support

The number symbolizes the surprising nature of Donald Trump's rise to front-runner status.

There’s never been a US presidential candidate like Donald Trump. Just how unusual has his candidacy been? In poring over some poll data Monday morning, we noticed one number that to us symbolizes the surprising nature of his rise to front-runner status.

That number reflects the percentage of Republican voters who have a favorable opinion of him, as a political person. Right now it’s 69, according to the most recent ABC News/Washington Post poll.

The size of the number itself isn’t what makes it surprising. Sixty-nine percent is pretty good for a favorability rating, but Mr. Trump isn’t the leader in this particular numerical category, according to ABC/Post data. That would be Ben Carson, who’s viewed favorably by 71 percent of Republican voters.

Its singularity lies in the fact that it used to be much lower. In July, Trump was viewed favorably by 57 percent of GOP voters in this same poll series. In May, prior to his announcement that he was going to actually run for president, the corresponding number was ... 23.

That’s right: Trump has tripled his favorability in his party since he started campaigning for the Oval Office. That’s while he’s been insulting rivals and past GOP nominees alike while battling with various news figures and blasting out many statements labeled questionable (at best) by fact-checkers.

By itself, such a rise isn’t completely startling. It happens all the time in presidential politics: An underdog candidate starts out with low favorability, since few people are aware of his or her strengths and faults. The candidate rises in favorability as he or she becomes better known.

But Trump was already famous, due to him being an celebrity over decades. His name recognition was probably close to 100 percent when he jumped in the race.

That means he’s actually changed people’s minds about his political prospects, at least in some parts of the GOP. That doesn’t happen often. As Jonathan Last notes recently in The Weekly Standard, this is one of the ways Trump’s run has “defied the laws of electioneering.”

How did he do this? Most likely, it has to do with the anti-immigration hard line he’s taken from the moment he entered the race. (It was during his announcement speech that he called Mexicans sneaking over the border “rapists,” after all.) As has been widely noted, Trump seems to have tapped into a wellspring of anti-immigrant feeling that's resentful of the GOP elite.

His favorable numbers built quickly after that. Since then, they’ve leveled off and bounced around.

But this is not – repeat, not – necessarily an indication of future electoral performance. Trump also has moderately high negative ratings in the GOP. Among Republicans, 29 percent hold an unfavorable view of The Donald, according to ABC/Post numbers. That means he has a hard core of supporters, but a hard core of opponents as well.

Among the electorate as a whole, Trump’s favorability numbers are so far underwater you’d need a bathyscaph to find them. Democrats (and to a lesser extent self-described independents) so dislike him that he has a 55 percent unfavorable, 37 percent favorable rating, according to HuffPost Pollster.