Donald Trump seemed to signal a new -- and even darker -- phase of his front-running campaign for the Republican presidential nomination Monday when he released a statement insisting that Muslims should be banned from entering the country under any circumstances "until our country's representatives can figure out what is going on."

Trump has been pushing the envelope for months now -- from his June campaign announcement in which he said Mexican illegal immigrants were "rapists" to his condemnation of John McCain as something short of a war hero to his made-up tale of "thousands" of New Jersey Muslims celebrating after the Sept. 11, 2001, attacks. And, with that ratcheting up of rhetoric, he has become increasingly dangerous for the party he is seeking to represent next November.

Now, with his "ban Muslim immigration" proposal, Trump has become a clear and present danger for a party that badly needs to re-position itself with non-white voters after two sweeping losses at the presidential level in 2008 and 2012. Trump, given his status at the front of the 2016 pack and his increasing willingness to adopt positions on the fringes of mainstream political thought, has the very real potential to cost Republicans up and down the ballot should he be the nominee.

And there's not a damn thing the party establishment can do about it.

"The challenge is that the 'establishment' sees that Trump gains strength when they call him out," said prominent Republican pollster Glen Bolger. "It still needs to be done, but the establishment is held in such low regard by the Trump/[Ben] Carson/[Ted] Cruz voters that they have no sway. None."

Bolger's right.  Trump has built his movement -- and, like it or not, it is a movement -- on his disdain for party leaders and politics as usual. His willingness to call his Republican rivals "stupid" and "losers" and to give party leaders the same level of deference he shows everyone else -- none -- has transformed the billionaire into a hero among a not-insignificant segment of the GOP.

For the party -- or one of its apparatchiks -- to attack him as having crossed over some sort of line of acceptable conduct would likely only serve to reinforce Trump-as-unpolitician. That's, of course, the very thing that drew people to him in the first place.

What's remarkable, however, is how little sustained incoming attack Trump has had to deal with -- either from his rivals or the party at large. Yes, John Kasich's super PAC has gone after Trump as dangerously inexperienced in ads. And, yes, every candidate -- or at least most of them -- condemned Trump's proposed Muslim immigrant ban tonight.

But, overall, Trump has been treated with kid gloves by a field that either wants to be the receptacle for his voters if/when the real estate mogul drops out (Cruz) or is simply afraid of the repercussions of attempting to take Trump down (everyone else). It's like they aren't even trying to stop what they all acknowledge is a massive and growing problem.

"It's simple, a candidate has to do it themselves," one high-level GOP operative, granted anonymity to speak candidly, said of the need to knee-cap Trump. "At the next debate, a candidate has to step up and hit him. It is a simple tactic, but difficult when you're standing up there on the big stage and have to really do it."

The necessity of bringing down Trump -- or at least trying to -- is likely to be driven home by Trump's latest comments. The question Republicans not named Trump will now have to face is whether it's too late to do what must be done to preserve the party's broader fortunes in 2016.  In refusing to go hard after Trump over the summer and discredit him before he grew into the political power he is today, did Republicans commit a mistake they won't be able to fix?

I asked one senior GOP strategist how the party establishment could somehow disarm Trump given his current status in the race and the lack of any leverage they have over the front-runner.

His answer? "Pray."