THE MORNING PLUM:

As the year draws to a close, and we prepare to turn a corner into 2016, most of the polling shows Donald Trump continues to dominate among Republicans. A CNN survey released this morning finds that Trump is supported by 39 percent of Republican and GOP-leaning independent voters nationally — more than double the 18 percent that Ted Cruz commands. Marco Rubio has slipped a bit, to 10 percent.

Notably, Trump holds overwhelming leads over his rivals when it comes to which candidate Republican voters prefer to handle the Islamic State and immigration:

— 47 percent of Republicans and GOP-leaners say Trump can best handle the Islamic State; 21 percent say that about Cruz; and four percent say that about Rubio.

— 55 percent of Republicans and GOP leaners say Trump can best handle immigration; 15 percent say that about Cruz; and 10 percent say that about Rubio.

Immigration and terrorism, of course, are the two issues around which Trump has delivered his ugliest and most xenophobic pronouncements and policy ideas, if you can call them that. Other polling has suggested that these issues have become intertwined with one another in the minds of Trump supporters. And the evidence suggests that Trump may have gained substantially among Republicans from the heightened climate of fear that developed in the wake of the Paris and San Bernadino attacks, the dates of which are marked with black arrows below:

After the Paris attacks, some Republicans suggested they welcomed the resulting focus on national security. Marco Rubio, for instance, said it was a “positive development” that Americans would now “confront more directly the issue of national security,” and while he subsequently clarified that remark, he also reiterated that the attacks had “refocused our campaign on what I think should be the number one issue in any federal campaign — especially for the presidency — and that is our national security.”

I continue to think it’s very unlikely that Donald Trump will win the GOP nomination. But some observers, such as former George W. Bush campaign adviser Matthew Dowd, are now flatly claiming he is the favorite. If he does somehow win, the charged atmosphere in the wake of the attacks arguably will have played a key role. Even if Trump doesn’t prevail, the attacks probably have already helped create fertile political ground for Trump to engage in maximum demagoguery about immigrant threats and Muslims, which is in turn forcing his GOP rivals to play catch-up to his bluster. Even some Republicans worry that this has dragged the GOP to a compromised place, and Democrats are operating from the premise that it will taint the party heading into the general election.

How crazy an outcome would it be if the focus on national security that Republicans themselves wanted ended up either (at best) maximizing the damage Trump does to the GOP or (at worst) helping to stick them with Donald Trump as the nominee?

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* TRUMP AND CRUZ BATTLE FOR THE SOUTH: Politico talks to a number of GOP operatives and strategists in southern states and discovers a widespread sense that Donald Trump and Ted Cruz are the frontrunners in the region, and that Marco Rubio is being left behind:

The feeling on the ground is that Cruz has the momentum with conservative activists and that there’s some true support behind Trump’s high poll numbers, much as many party stalwarts wish otherwise. And while Rubio is generating considerable interest among more centrist Republican voters, he’s being squeezed not just on the right by Cruz but in the moderate lane by Jeb Bush and Chris Christie.

Well, that’s inconvenient for Republican leaders, isn’t it!

* AMERICANS OPPOSE MUSLIM BAN, BUT REPUBLICANS ARE MORE DIVIDED: A new Quinnipiac poll finds that Americans oppose “banning people who are Muslim from entering the United States by 66-27. Among Republicans, those numbers are 51-41 — which means four in 10 of them favor it.

Also, the poll finds that Republicans believe by 47-39 that mainstream Islam encourages violence against non-Muslims. (Americans say it is a peaceful religion by 55-28.) All of this again suggests we should reckon with at least the possibility that a lot of Donald Trumps supporters are rallying to him in part precisely because of his xenophobia.

* AMERICANS WANT WAR, WAR, WAR! The new Quinnipiac poll also finds that Americans say by 52-40 that the U.S. should send in ground troops to fight the Islamic State, and of those who want this, a majority says the number of troops should be “significant.”

Meanwhile, 82 percent say there is likely to be a terrorist attack in the U.S. causing “large numbers” of deaths in the “near future.”

* REPUBLICANS NOT CONCERNED ABOUT CLIMATE CHANGE: The Quinnipiac poll also finds that 66 percent of Americans are very or somewhat concerned about climate change. By contrast, Republicans are not concerned by 64-37. And yet, Republicans say by 47-44 that they want to see the next President support policies to combat climate change. So that’s something.

* WAIT — DO REPUBLICANS SUPPORT PARIS CLIMATE DEAL? A new Reuters poll seems to suggest as much:

More than half, or 58 percent, of Republicans surveyed said they approved of U.S. efforts to work with other nations to limit global warming, the poll showed. Forty percent said they would support a presidential candidate who did so.

Of course, even if this is right, the GOP presidential candidates will probably play to the GOP voters who oppose action, and will likely pledge to withdraw the U.S. from the global accord, as Ted Cruz has already done.

 * RUBIO’S BOAST ABOUT OBAMACARE, DEBUNKED: Post fact checker Glenn Kessler does a major demolition job on Marco Rubio’s ongoing boast that he dealt a staggering blow to Obamacare by killing its insurance company “bailout” provision. It’s complicated stuff, but the rub is this:

Rubio goes way too far in claiming credit here. He raised initial concerns about the risk-corridor provision, but the winning legislative strategy was executed by other lawmakers. He certainly had a more central role in the immigration bill from which he has distanced himself — which may be a reason he is trying to elevate his role in this case.

That’s a great point: If we’re going to be talking about Rubio’s legislative accomplishments, he deserves a whole lot more credit for his role in shepherding Schum-Obamnesty through the Senate!

* HILLARY BLASTS TRUMP’S VULGARITY: Hillary Clinton unloads on The Donald in an interview with the Des Moines Register:

“I really deplore the tone of his campaign, the inflammatory rhetoric that he is using to divide people, and his going after groups of people with hateful, incendiary rhetoric. Nothing really surprises me anymore. I don’t know that he has any boundaries at all. His bigotry, his bluster, his bullying have become his campaign. And he has to keep sort of upping the stakes and going even further.”

As noted yesterday, this also has the effect of elevating Trump, enabling him to spread more damage inside the GOP. The Clinton camp is using him to tar the rest of the GOP candidates (who are trying to keep pace with his bluster) as reckless and dangerous.