A new CNN poll finds that Bernie Sanders is surging among Democrats nationally — Hillary Clinton leads him by 47-29, but her support has slipped nine points since July, while Sanders’ backing has climbed 10 points. It’s hard to know how much national polling at this juncture matters, if at all, but one thing seems clear: The Clinton camp is taking the Sanders threat seriously.

And in this sense, Sanders might be doing Clinton a big favor. Take a look at this new ad that the Clinton campaign is running in the early-voting states of Iowa and New Hampshire, backed by a $2 million buy:

The ad leans into a populist message at the outset. Clinton says:

“When you see that you’ve got CEO’s making 300 times what the average worker’s making, you know the deck is stacked in favor of those at the top. I want it to be back where it was when I came of age. Where my mom who never got to go to college could see her daughter go to law school. We need to have people believing that their work will be rewarded. So I’m going to be doing everything I can to try to get that deck reshuffled, so being middle class means something again.”

Anne Gearan reports that Clinton has been repeating versions of this message in all sorts of settings. One clue as to why can be found in the CNN poll’s internals: Among liberals, Sanders is either tied with Clinton or doing better than she is on economic questions.

The poll finds that liberal Dems are split on which candidate can better handle the economy, with 41 percent favoring Sanders and 40 percent favoring Clinton. And Sanders leads Clinton by 49-36 among liberals on who would best handle the gap between rich and poor. Sanders’ robust agenda to combat inequality may be resonating.

That doesn’t mean Clinton is in serious danger of losing the primary battle. As Nate Cohn notes, Sanders’ support is largely confined to the white progressive left, which will enable him to compete in states like Iowa and New Hampshire. Clinton’s support is far more diverse — it is strong among women, African Americans, Latinos, and moderate and conservative Democrats, a more viable coalition for winning the Democratic nomination. Liberal support for Sanders on the economy is consistent with this.

But it does seem as if Sanders’ presence may be forcing Clinton to sharpen up her own populist message. And, crucially, she seems to be trying to develop a message to Dem primary voters that could also resonate in a general election. After all, Clinton’s message right now carries echoes of the economic pitch that helped Obama win the 2012 general election: The economy is rigged in favor of the rich and against the middle class; being middle class no longer means what it used to mean; an active policy response is required to restore economic fairness and make work pay again.

No matter how many times pundits assert that Clinton has lurched sharply to the left, it just isn’t true: She is running as a mainstream Democrat, and she has not embraced key elements of the Sanders/Elizabeth Warren economic agenda. If Sanders is forcing Clinton to hone an economic message that resonates with both a primary and general election audience — and we’ll likely see more pressure to do this in the Dem debates this fall — it can only help.

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* A STRUGGLING SCOTT WALKER SEEKS TO REGAIN GROUND: The Post reports on a conference call that Scott Walker held with top supporters to explain why he’s trailing in polls nationally and in Iowa, and how he plans to turn things around:

“We need to step it up and remind people that we didn’t just take on the unions and Democrats, we had to take on my own party establishment, those who did not want to take on the status quo,” Walker said on the call….Walker now intends to focus his energy primarily on challengers from the right — a constituency that is particularly important in the first-in-the-nation Iowa caucuses.

Months of boasting about crushing unions and liberals don’t seem to be doing the trick; now he’ll vow to hulk-smash the GOP establishment, in a bid for Donald Trump voters.

* BREAKING: TRUMP NOW COMPETITIVE IN GENERAL ELECTION!!! The new CNN poll also finds that Donald Trump is only trailing Hillary Clinton in a head-to-head match-up by six points among registered voters, 51-45 — he’s doing as well or better against her than all his GOP rivals.

While polling this early has little predictive value, you have to wonder whether this sort of finding will only encourage Trump to stick this out for as long as possible — and perhaps even run as a third party candidate.

* HILLARY LEADS GOP RIVALS: The new CNN poll also finds that Clinton leads Jeb Bush by 52-43; she leads Scott Walker by 52-46; and she leads Carly Fiorina by 53-43. Surely these findings will get as much attention as did recent polls showing her negatives high, leading to a fusillade of “Hillary spiraling out of control” stories.

 * BUT HILLARY’S NEGATIVES REMAIN HIGH: Speaking of all those stories about her high negatives, the CNN poll also finds this: 56 percent say Clinton did something “wrong” by using a personal email as Secretary of State.

* AMERICANS SUPPORT FUNDING PLANNED PARENTHOOD: A new Reuters/Ipsos poll finds that the GOP drive to defund Planned Parenthood may not prove popular:

Americans broadly support providing federal funding for free women’s health exams, screenings and contraception services…Democrats and Republicans supported federal funding for the services, even when Planned Parenthood was named. Overall, 54 percent of those in the poll supported federal funding of Planned Parenthood, and 26 percent opposed it.

Well, sure, but all that matters are the views of Republicans who oppose the funding. Duh!

* TEA PARTY PSYCHED ABOUT TRUMP’S IMMIGRATION PLAN? The Wall Street Journal reports that Latino conservatives are appalled by Trump’s new immigration plan. But Tea Partyers may like it:

Many in the GOP disagree with Mr. Trump, but his ideas also have a base of support. “His immigration plan will resonate with a broad cross-section of grassroots voters, particularly tea-party and conservative voters,” said Mark Meckler, a nationally known tea-party-aligned activist.

Now that Trump has unveiled an immigration plan with genuine specificity, we will be able to track whether Tea Partyers and conservatives agree with it.

* AND THE QUOTE OF THE DAY, GOP-CATTLE-CAR-CAUCUS EDITION: Senator Lindsey Graham on Cattle-Car-Caucus leader Donald Trump’s vow to deport all undocumented immigrants:

“You’re not going to get 11 million people and drive them back out of this country,” he said. “That’s just not practical. That’s going to kill the Republican Party.”

Not practical? But Trump is a businessman. He can compel our political system to do anything.