Republican presidential hopeful Donald Trump speaks at his South Carolina Campaign Kickoff Rally in Bluffton, S.C., Tuesday, July 21, 2015. Donald Trump wouldn't apologize after questioning whether Sen. John McCain -- who spent five years as a prisoner during the Vietnam War -- is a war hero. (AP Photo/Stephen B. Morton)

It has taken a long time, but even Democrats are starting to realize that Donald Trump is not a sideshow but the main event in the GOP presidential race.

Explanations for his enduring appeal fall into two rough categories: his personality and his politics. Some people not only love his ideas, but they also love the way that he delivers it.

Charisma plus a powerful message has always been the formula for political success. Those who doubted Trump for so long perhaps didn't recognize that he had a special brand of both.

Here are four basic reasons that explain Trump remains so popular among some Republicans.

1. Trump has simple answers for everything

Trump is often wrong, but what matters is that he always sounds right. In politics, force of character can be as important as facts (which nobody can agree on anyway). Trump’s charisma, his confident and decisive air, forms a huge part of his appeal, psychologists told my colleague Max Ehrenfreund:

"They're responding to dynamism, to force, to movement, to smiling, to facial expressions that convey authority," said Stanford psychologist Jeffrey Pfeffer. Trump "does it with more force. He does it with more energy. Energy is contagious."

Combine that supreme confidence with simple, intuitive answers that resonate with voters on a deep level. The result is a psychologically intoxicating mix. If you don’t like immigration, build a wall. If you’re suspicious of Muslims, track them in a database. If you support police officers, impose the death penalty on cop killers.  

These are thrilling ideas to many voters, especially when a candidate like Trump articulates them with such authority.  

"People like the idea that deep down, the world is simple; that they can grasp it and that politicians can't," John Hibbing, a psychologist at the University of Nebraska, told Wonkblog. "That's certainly a message that I think Trump is radiating."

2. A lot of people dislike immigrants

Trump supporters are particularly attracted to his views on immigration. He’s hugely popular among people without college degrees, who have been left behind by economic progress in recent years. Many of these people blame immigrants for their own poor prospects, since they compete for some of the same kinds of jobs. As my colleague Jim Tankersley writes:

Non-college grads have struggled since the turn of the century: Economist Robert Shapiro estimates that incomes stagnated or declined from 2002 to 2013 for American households headed by workers without a degree, a marked departure from prior decades.

By more than a 2 to 1 margin, Republicans who supported Trump in the poll said immigrants weaken society. That’s the opposite view of Americans overall, who said by a 25-point margin that immigrants mainly strengthen America.

(To get a sense of how those groups overlap, Republicans without college degrees are 19 percentage points more likely to say immigrants weaken American society than Republicans-leaning college graduates.)

And it’s not just an economically-frustrated slice of America that is attracted to Trump’s ideas. Nearly half of registered GOP voters agree with him that undocumented immigrants should be deported, and that America should turn away refugees. This is a passionate base. They believe Trump is electable and will make a difference.

3. People are sick of the political establishment

The more Trump is criticized, the more popular he seems to get. As my colleague Dave Weigel reported yesterday from a focus group of Trump supporters, nothing seems to be able to put them off their candidate. In fact, when rivals attack him, Trump’s numbers go up:

That confidence only grew as Trump’s alleged gaffes and mistakes were laid out. At 6:30 p.m., when the session began, all 29 participants were asked to rate their likelihood of voting for Trump, and just 10 people said they were at nine or 10. After one hour of mostly negative questions about Trump, six more people joined that confident group.

“I’ve been talking about negatives, and you’re up on him!” said an astounded [Republican pollster] Frank Luntz. “That’s the story of Trump’s poll numbers.”

Trump has positioned himself as the anti-elite candidate, which to some voters has made him more or less immune to criticism from the mainstream parties or the mainstream media. When the press slams him for saying shocking (and often untrue) things, that only heightens the us vs. them dynamic.

There have always been anti-establishment presidential contenders, of course. The fact that Trump been so singularly successful perhaps has less to do with him and more to do with this political moment. From the Tea Party surge in 2010 to the present you can trace an arc of mounting impatience among voters in part of the GOP. That pent-up frustration may be finding its moment — and its voice — right now, in Donald Trump.

4. He says things that people have been afraid to say

A lot has been made of Trump’s ability to shrug off gaffes. He often makes insensitive or factually wrong statements that in the past would have torpedoed any other candidate’s prospects.

Instead, his comments — about some Mexicans being rapists and blood coming out of Megyn Kelly’s “wherever,” or his incorrect claim that "thousands’"of Muslims in New Jersey celebrated 9/11 — have had virtually no impact on his popularity in the polls

In October, New York Times TV critic James Poniewozik wrote a provocative piece arguing that the key to understanding Trump’s success lies in understanding the attention economics of modern media. Trump, well-rehearsed in the high-key registers of reality television, brings to the race a savviness about what keeps people glued to their screens:

Traditional presidential politics is like television in Ed Sullivan’s day, when the big three networks developed the idea of “least objectionable programming” — broad, inoffensive, something-for-everyone shows intended to keep anyone from changing the channel.

Reality TV, like Mr. Trump’s campaign, is a product of a fractious time of niche audiences. When there are hundreds of entertainment outlets, “least objectionable” is death: You need to stand out.

It's not just that Trump is willing to be provocative — he's exciting to many people because he says the things they feel they can't say.

"I think the big problem this country has is being politically correct," Trump said at the Cleveland GOP debate in August. "I’ve been challenged by so many people and I don’t, frankly, have time for total political correctness."

As one supporter explained during another focus group session: “When Trump talks, it may not be presented in a pristine, PC way, but we’ve been having that crap pushed to us for the past 40 years! He’s saying what needs to be said.”