Front-Runner Donald Trump may just have crossed a line, one that can’t be un-crossed.

Back before the Iowa Caucus, on January 29th, I wrote here in American Thinker that there were only two possible Trump-Killers: 

1.    A failure of his crowds to turn out and vote; and,

2.    Saying something that was clearly beyond the pale: something more outlandish or confrontational than Republican voters are willing to accept -- or ignore

Clearly, the first potential Trump-Killer was a non-starter.  His crowds at rallies have indeed turned out to also be crowds at the ballot box.  However, the other potential Trump-Killer -- that Trump would finally say something so outlandish that he’d turn off voters -- remains to be seen.

Unless, of course, what we just saw in the South Carolina debate Saturday night, a week before the South Carolina primary, proves to be that Trump-Killer.

What did we see?

We saw Trump embracing and advocating two related positions that only Ron Paul’s more extreme libertarian conspiracy-theory supporters -- or Michael Moore bomb-throwing Democrats -- had previously adopted. Trump’s 9/11-bombshell was a one-two punch that either won the support of really unhappy Republicans -- or completely put-off conservative Republicans. 

This potential Trump-Killer incident began with Trump once again asserting that he did not support the Iraq invasion in 2003, which he deemed a mistake.  That, in itself, is not a problem.  Many Republicans now see that attempts at nation-building, such as President Bush tried in Iraq, are a mistake.

But then Trump issued a pair of charges that may well have gone too far.  Maybe way too far. 

First, The Donald made it clear that he thought Republican President George W. Bush actually lied about there being Weapons of Mass Destruction in Iraq -- and did so in order to gain support for the invasion of Iraq in 2003.  Facts following the invasion seem to prove that the fears of WMDs in Iraq were either overblown, or the intelligence findings of the CIA, British and Russian intelligence were all completely wrong.  However, until now, it took a Michael Moore-like extremist to accuse the President of lying for the purpose of dragging America into a war that few -- beyond the President himself -- actually wanted to fight.

That conspiracy theory-like one-two punch, which normally gets thrown only from from the far left -- or the far right -- might cross a line.  Especially in South Carolina, where the former President remains quite popular.

Trump initiated the dustup, initially with Jeb Bush, calling him out for his indecision on the Iraq War.  Trump reminded Jeb that, after he announced for President, the former Florida Governor took the better part of a week to decide on a position about the Iraq war. That was a stumble that marred his campaign launch, an unforced error that has haunted the First brother ever since.

Bush didn’t take this attack lying down, defending his brother by swinging back hard at Trump:

"While Donald Trump was building a reality TV show, my brother was building a security apparatus to keep us safe. And I'm proud of what he did."

Trump then raised the stakes -- and might have just crossed a line that can’t be un-crossed:

"The World Trade Center came down during your brother's reign. Remember that." *

Trump was charging that, because 9/11 happened during his Presidency, George W. Bush had not actually kept America safe.  This is a claim that has been made before, but generally by acolytes of Michael Moore or conspiracy-theory supporters of Ron Paul -- extreme liberals and hard-core Libertarians -- but not by anybody “mainstream.” 

Until now.

Remarkably, Trump's made this argument before.  Back in 2015, he told Bloomberg TV,

"When you talk about George Bush, I mean, say what you want, the World Trade Center came down during his time."

However, that interview -- one of hundreds of interviews Trump has given since announcing -- didn’t catch a lot of media or voter attention at the time.  But this is the first time that Trump has made this extreme argument on the debate stage. 

He was instantly challenged by Marco Rubio -- who defended George Bush far more passionately than did his own brother Jeb.  As he often does when challenged, Donald Trump then doubled-down.  When the Florida senator said that George W Bush “kept us safe,” Trump challenged him by once again blaming the 9/11 World Trade Tower terror disaster on George W. Bush.

"How did he keep us safe when the World Trade Center came down?  I lost hundreds of friends, the World Trade Center came down during the reign of George Bush.  That is not safe, Marco, that is not safe,"**

The crowd was not packed with Trump supporters -- he blames this on lobbyists and big-money donors, and considering his lead in the polls, he might be right.  Yet the hall was not exactly packed with Bush supporters, either, yet when Trump dropped his 9/11-bomb, the audience was decidedly hostile.

Whether this hostility carries over to the voters -- in South Carolina, first, then in Nevada and the upcoming “SEC” Super Tuesday primary states -- remains to be seen.  The “smart money” has written Trump off several times for outlandish things he’s said -- about Muslims and Mexicans.  But now he -- as a Republican -- has blamed a terror attack on a Republican President.

That may be more than Republican primary voters can tolerate.  That might indeed by the Trump-Killer.

Ned Barnett, owner of Barnett Marketing Communications in Las Vegas, has handled media and strategy on three state-level Presidential campaigns, as well as dozens of Congressional, Senatorial and other campaigns.  He has taught at two universities and published a dozen books on professional communications.  When he’s not commenting on politics, he supports a range of high-tech, start-up, healthcare and issues-advocacy clients.  He is currently working on a practical, how-to book on winning election campaigns.

* Transcript quoted from Vox.

** Transcript quoted from Mother Jones.