Republican presidential candidate Donald Trump speaks during a campaign event in Myrtle Beach, S.C., on Tuesday. (Willis Glassgow/AP)

Donald Trump’s offensive comments and flat-out falsehoods just keep coming.

Yet the celebrity billionaire continues his unlikely reign as the front-runner of the 2016 GOP presidential field. Which raises the question: Will Trump eventually cross the line — or is he proof that lines no longer exist?

The political world is beginning to conclude that no one will know the answer to that question until Republicans actually start voting in February.

It increasingly appears that the GOP electorate may be the party’s only remaining means of stopping him, as voters begin to imagine what it would be like to have Trump as their standard-bearer, or maybe even in the White House.

To date, however, his flame­thrower rhetoric has seemed to make his supporters love him all the more.

Here are the most surprising moments from Republican presidential candidate Donald Trump's rambling speech in Fort Dodge, Iowa on Nov. 12. The candidate spoke for more than an hour to an audience at Iowa Central Community College. (Sarah Parnass/The Washington Post)

“There’s almost no limit” on what he can say, said Frank Luntz, a pollster who gained fame as a phrase­­maker for Republicans. “You cannot bring him down by what he says or what he thinks.”

The Trump phenomenon is a chicken-and-egg conundrum. He is both a manifestation and a catalyst of an increasingly coarse and angry political culture, a Father Coughlin for the social-media era.

“I don’t think Trump can be explained as if he arose out of nothing. He didn’t create this moment, as much as he is a product of it,” said Peter Wehner, who wrote speeches and ran the policy idea factory in George W. Bush’s White House. “There’s an environment that allowed him to arise. But having arisen, and being who he is, he has kept pushing the boundaries and knocking down one guardrail after another.”

GOP elders find some comfort in the fact that — at least, so far — there seems to be a ceiling that limits how high Trump can fly. In most national and state polls, his support level is running no higher than the mid- to high 20s. That backing comes primarily from older, less-educated white voters.

They are the aggrieved, who say they barely recognize the America in which they are living.

“Trump is a loud­mouthed person, yes, and he does sometimes just say things to women to hurt their feelings,” an Indiana woman said during a late-October focus group of GOP primary voters conducted by the Annenberg Public Policy Center of the University of Pennsylvania.

At a rally in Columbus, Ohio, Republican presidential candidate Donald Trump told the audience in response to whether he would approve waterboarding, "You bet your ass I would." (Reuters)

“But I’m going to stick with my belief saying that he’s going to try his best to get the country back the way our Founding Fathers had it at one time,” she added.

Comments that would have disqualified candidates in an earlier era have been lauded by Trump’s following as proof of his authenticity against the forces­ of political correctness.

“Essentially, it is the culture of the blog world and social media,” said Democratic pollster Peter Hart. “I do believe that we are in a different era. It is an era where people’s immediate emotions and reactions overwhelm the basic principles of a democratic society.”

Trump’s apparent strength, however, may dissipate, once he gets out of the over­heated atmosphere of a crowded Republican primary.

He has been able to hold the lead with less than one-third of the party behind him only because there are more than a dozen GOP presidential candidates running.

What remains to be seen is whether the majority of Republican voters will consolidate around someone besides Trump — the only way for him to lose the nomination.

In the meantime, Trump has “crossed the line for a general-election electorate and made himself all but unelectable in a general election,” said Matthew Dowd, who was chief strategist for Bush’s 2004 reelection campaign.

Democratic front-runner Hillary Clinton sees Trump’s rise as an opportunity to tarnish his entire party.

“He has been dealing in prejudice and paranoia, and that is bad for our politics and our country,” the former secretary of state said in a Facebook chat Tuesday sponsored by the Spanish-language television network Telemundo.

“Do not forget that if you look at their policies, most of the other Republican candidates are equal to Trump without his or her hair­style,” Clinton added.

Just a partial list of those whom Trump has insulted would include immigrants, women, Iowa voters and prisoners of war.

He has justified violence against a Black Lives Matter protester at one of his rallies, advocated surveillance of mosques and fabricated an episode in which he claimed thousands of New Jersey Muslim Americans celebrated the toppling of the World Trade Center on 9/11.

He also retweeted false data claiming that African Americans are responsible for the vast majority of murders of both blacks and whites. The source was a “crime statistics bureau” that does not appear to exist.

Trump has also said he would bring back water­boarding and “more than that” in questioning those suspected of terrorist ties.

“It works,” Trump said of the interrogation technique that many regard as torture. “Believe me, it works. And you know what? If it doesn’t work, they deserve it anyway, for what they’re doing.”

At the same time, his ferocious rhetoric has opened a space for other GOP contenders to say things that they might not have in a Trumpless environment.

Nowhere is that more evident than on the question of whether to allow Syrian refugees into the United States.

Retired neurosurgeon Ben Carson has compared them to dogs, some of which may be rabid. Both former Florida governor Jeb Bush and Sen. Ted Cruz of Texas have suggested a religious test, in which Christian Syrians would be allowed into this country while Muslims would be barred or subjected to greater scrutiny.

“There is very little discussion of what it means for the Republican Party to become a nativist, protectionist party. That is where Trump is taking us,” said Vin Weber, a former Minnesota congressman and veteran GOP strategist who is supporting Bush.

His opponents — most notably of late, Ohio Gov. John Kasich — have taken a few swings at Trump and largely missed. In part, they all face the same problem, which is that any criticism of him only validates his standing as the GOP establishment’s worst nightmare.

In the 1950s, Sen. Joseph McCarthy (R-Wis.) conducted a witch hunt for communists that came to an end only when a Boston lawyer, Joseph Welch, challenged him on national television with the question: “Have you no sense of decency?”

But there is no apparent figure on the scene now who would have the capacity to do that to Trump.

Which leaves another alternative.

“The primary process will either legitimize what Trump is doing and strengthen his case and accelerate this descent, or the voters will say no to it,” Wehner said. “He’s got to be repudiated in the voting booth.”