This new poll finding, courtesy of CNN, is not all that surprising, but it is very illuminating of the demographic challenges the GOP faces right now: A big majority of Republicans believes that the government’s main focus on immigration should be not just on stopping the flow of illegal immigrants, but also on deporting those already here.

The poll asks:

What should be the main focus of the U.S. government in dealing with the issue of illegal immigration — developing a plan that would allow illegal immigrants who have jobs to become legal U.S. residents, or developing a plan for stopping the flow of illegal immigrants into the U.S. and for deporting those already here?

By 56-42, Americans support developing a plan to legalize undocumented immigrants over stopping their flow and deporting those already here. Independents agree by 58-39, and moderates by 59-40.

But Republicans favor stopping the flow of undocumenteds and deporting those already here by 63-34. So do conservatives, by 55-43. “Those already here,” of course, amount to some 11 million people.

Now, it’s certainly possible that GOP support for deportation is inflated somewhat by the inclusion of securing the border on that side of the question. But even when the question is framed a bit less starkly, as a recent Post/ABC News poll did, a majority of Republicans does not think the undocumented should be allowed to live and work here even if they pay a fine and meet other requirements. This should not obscure the fact that a substantial number of Republicans are, in fact, open to legalization; it’s just that more of them apparently aren’t.

And as such, what the CNN numbers again confirm is that there is a deep and intractable divide between the two parties on what to do about the undocumented population. This fundamental underlying difference matters far more than Donald Trump’s vicious rhetoric, which (assuming he doesn’t run as a third party candidate) will likely prove ephemeral.

Indeed, the CNN poll hints at the demographic challenge the GOP will face after Trump fades and the only person still listening to his bluster is his reflection in the mirror. As Brian Beutler recently observed, the GOP effort to grapple with the Trump phenomenon without alienating his supporters throws into stark relief the basic divide among the GOP presidential candidates over how to get to the White House. Some (Jeb Bush) are arguing for a genuine effort to broaden the party’s appeal outside its core constituencies, while others (Scott Walker) are seemingly betting it all on an ability to energize still more Republican-friendly white voters. As Beutler argues, the rise of Trump illustrates in particularly harsh terms that Republicans may have to choose one or the other.

Indeed, if the CNN poll is right — and a big percentage of Republicans favors not just securing the border, but also deporting all of the undocumented — then it could prove very hard to do the former without alienating too many of the latter voters. (The CNN numbers also indicate that majorities of white evangelicals and older voters, i.e., GOP-friendly constituencies, favor securing the border/deportation.) Some GOP pollsters have argued that GOP voters can be won over on legalization, if they are led through the moral and practical complexities of the issue. I like to believe that is true. And I hope Jeb Bush puts it to the test. But it could prove very difficult to pull off; the CNN poll suggests that since 2012, Republican voters on immigration may have only lurched rightward.

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* HILLARY ROLLS OUT CLIMATE PLAN: Hillary Clinton is introducing a plan to install more than half a billion solar panels nationally by the end of her first term, and in the process, she’s ridiculing the ubiquitous climate-skeptical claim from Republicans that “I’m not a scientist”:

“I’m just a grandmother with two eyes and a brain and I know what’s happening in the world will affect my daughter and especially my granddaughter,” she said.

Clinton is also vowing to protect Obama’s rules curbing carbon emissions from existing power plants. The battle over those rules — and over U.S. participation in a global climate deal — will help frame the forward-backward contrast between the two parties in 2016.

* SOME REPUBLICANS HOLD BACK IN HILLARY EMAIL FLAP: The New York Times catches a fascinating dynamic: While Scott Walker is calling for a probe of the latest Hillary email revelations, Marco Rubio is treading more carefully and Jeb Bush has said nothing:

In part, their reluctance was a reaction to the complexity of the email controversy. But it also appeared to reflect the thinking of campaign operatives and outside groups that are looking past the Republican primaries and toward a general election race against a woman who has often benefited from rivals who swung too hard.

Folks with long memories may recall that the Clintons have been known to successfully convert attacks on them into negatives for their opponents, by portraying them as zealous overreach.

 * HOUSE DEMS WHIPPING FOR IRAN DEAL: Politico’s Lauren French and John Bresnahan have a useful inside look at how Dems are rounding up support among House Democrats for the Iran deal. This is interesting:

The whips are also working members over with a blunt political message: Come out in support now and save yourself from a painful August….Any on-the-fence Democrat should expect AIPAC and its coalition of pro-Israel groups to use the August break to their advantage. Beyond the television and Internet ads, the group will capitalize on its national network of allies to apply consistent pressure on lawmakers to vote against the nuclear agreement.

With 150 House Dems already signing a letter backing diplomacy, watch for more of them to declare support for the deal itself before August.

 * MEDICARE TURNS 50 THIS WEEK: Paul Krugman takes stock of Medicare’s first half century, and explains why Republicans such as Jeb Bush and Paul Ryan continue to vow to “reform” the program by converting it into a voucher system:

The real reason conservatives want to do away with Medicare has always been political: It’s the very idea of the government providing a universal safety net that they hate….But when they make their case to the public they usually shy away from making their real case….What Medicare’s would-be killers usually argue, instead, is that the program as we know it is unaffordable…The underlying premise here is that…the only way to keep health care affordable going forward is to rely on the magic of privatization.

One presumes that all of the GOP presidential candidates will embrace Paul Ryan’s Medicare “reforms,” which (you may recall) were also a key point of contention in the 2012 campaign.

* GOP’S FAVORABLE RATINGS SINK: A recent Pew poll found the GOP’s favorability rating had sunk to 32 percent. E.J. Dionne breaks down the numbers and explains what they mean:

When Pew broke down these numbers at my request, the polarization in the electorate across so many demographic lines was sharp: Those with favorable opinions of the Republicans were overwhelmingly white (72 percent) and tilted conservative (52 percent). Those favorable toward the Democrats were more racially and ethnically diverse (only 55 percent white) and less likely to be conservative (20 percent).

Have we mentioned that the white share of the vote is projected to continue dropping in 2016?

* THE-DONALD-MENTUM RAGES IN IOWA AND NEW HAMPSHIRE!!! New NBC News-Marist polls find that Trump is running strong in the early nominating states of New Hampshire and Iowa:

Trump leads the Republican presidential field in New Hampshire, getting support from 21 percent of potential GOP primary voters. He’s followed by Jeb Bush at 14 percent, Scott Walker at 12 percent and John Kasich at 7 percent. In Iowa, Walker and Trump are in the Top 2 — with Walker at 19 percent among potential Republican caucus-goers and Trump at 17 percent.

Meanwhile, RNC chair Reince Priebus claims, hopefully, that he doesn’t think Trump will run as a third-party candidate.

* AND GIVE US MORE DONALD TRUMP, REPUBLICAN VOTERS SAY: Another CNN poll released over the weekend show that Republican voters want Trump to keep on runnin’:

Among Republicans and Republican-leaning independents who are registered to vote, 52% say they want Trump to stay in the race for the party’s nomination, while 33% hope that he drops out. Another 15% say they’d like to see him make an independent run for the presidency.

This poll was conducted entirely after Trump’s comments about John McCain. Also note that 15 percent — could that be enough to persuade him to make a third-party run?