Jeb Bush’s comments about immigration, and the continuing backlash to them, have produced a seminal moment in this debate, because they lay bare the fundamental difference between the two parties on the issue with remarkable clarity. It is this: Most Democratic lawmakers want the 11 million undocumented immigrants in this country to become a part of American society, while most Republican lawmakers want them to (at best) remain in the shadows of illegality or (at worst) leave.

To be sure, after the official party-wide GOP position of self-deportation (as expressed by the GOP presidential nominee) led to historic losses among Latinos in 2012, many leading Republicans agreed something needs to be done to legalize the 11 million. A handful of GOP Senators voted for the Senate bill and its special path to citizenship. Some are suggesting alternatives, such as legalization with no possibility of citizenship.

But for all practical purposes, the basic fact remains: House Republicans have not offered, or voted on, any formal proposal to confer on the 11 million any kind of legal status. So their de facto position is either the status quo or deportation (self-administered or otherwise). Reform’s fate turns on the core question of whether there exists any set of conditions or terms that can induce a sizable enough bloc of House Republicans to support some form of legalization for those 11 million people.

The Jeb Bush comments are important precisely because they illuminate the moral and political dilemma for Republicans that underlies this core question.

Speaking to conservative activists in New Hampshire over the weekend, Donald Trump elicited boos when he castigated Bush’s remarks. It’s worth rerunning Bush’s comments, because one of the most important aspects of them has not gotten enough attention — his suggestion that undocumented immigrants might have something valuable to contribute to American society if they are legalized:

“Yes, they broke the law. But it’s not a felony. It’s an act of love. It’s an act of commitment to your family…it shouldn’t rile people up that people are actually coming to this country to provide for their families. And the idea that we’re not gonna fix this with comprehensive reform ends up trapping these people when they could make a great contribution for their own families, but also for us….they can make a contribution to our country if we actually organized ourselves in a better way.”

Republicans who have responded to Bush with more nuance than Trump have accepted the former point but not the latter one. Rand Paul said: “People who seek the American dream are not bad people, but that doesn’t mean you can invite the whole world to come.” Ted Cruz responded that we need to be a nation that “welcomes and celebrates legal immigrants,” but that “rule of law matters.”

Neither Paul nor Cruz can accept Bush’s latter point, which is that an acknowledgment of the moral ambiguity surrounding the plight of illegal immigrants should open the door to another realization: Solving this problem in a smart way and integrating the undocumented into society is the best outcome for the country – even if they are, in fact, lawbreakers. For many Republicans, that’s the hard part to accept.

Let me reiterate that I’m sympathetic to the idea that it’s genuinely hard for Republicans to accept legalization in any form. The GOP position only two years ago was self-deportation. There are many motives for opposing legalization for the 11 million, but for many Republicans, opposition to rewarding lawbreaking is a matter of deeply held belief — it violates fundamental principles of fairness – and as such, amnesty is just not something they can bring themselves to accept on any terms.

Bush’s comments issue a moral challenge to Republicans to move beyond this view. He’s not simply saying the motives of illegal immigrants are morally complex and even understandable. He’s asking them to cross the Rubicon from there to a place where Republicans can reconcile themselves to the integration of them into American society as a morally tolerable outcome — indeed, as a practical and desirable one.

Before you rail at me for placing all the onus on Republicans to evolve on the issue, please remember that this is what the House GOP leadership’s own immigration principles also implicitly ask Republicans to accept. They say undocumenteds should be able to “live legally and without fear in the U.S.,” provided they pay fines and back taxes, and provided enforcement triggers are met. These principles unleashed a conservative backlash, and Boehner shelved reform. This again underscores that, as of now, there is no set of conditions or terms (no specific set of punitive hurdles to clear; no specific or workable set of enforcement triggers to meet) that has yet been suggested or proposed that can get enough Republicans to accept that outcome.

Perhaps Dems would ultimately not accept a compromise that entails accepting legalization without a special pathway to citizenship. I don’t believe that — I think Dems would accept one, and I’ve laid out a roadmap to that outcome right here. But the point is, we cannot ever move in that direction at all until Republicans show us how — or whether – they can ever accept any kind of legal status for the 11 million.

That’s basically the challenge implicit in Jeb Bush’s comments, only he packaged that challenge with an implicit critique of the moral failings of his own party on the issue that was unusual coming from a Republican of his stature, sparking outrage. The bottom line is we just don’t know how many Republicans are willing to meet Bush’s challenge. And we may not find out the answer for a long time to come.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.