CHARLESTON, S.C. -- Hillary Clinton's plan to stem her slide against Bernie Sanders in the presidential primary began to come into clear focus Sunday night in the fourth Democratic debate.

With two weeks to go before Iowa's caucuses, the former secretary of state offered several closing arguments:

• If you liked Barack Obama, stick with Clinton.
• Sanders is too risky, he'll jack up your taxes, and what he wants to do can't get through Congress anyway.
• Clinton is the only seriously electable Democrat in the race, regardless of polls that show otherwise at the moment.

She also went hard at Sanders, a Vermont independent senator, as too conservative on gun control and too radical on health care. With Sanders now tied with Clinton in Iowa, and leading in New Hampshire, her campaign is hoping that although Democratic primary voters may be in love with Sanders, they'll ultimately settle down with the pragmatic choice.

"We're at least having a vigorous debate about reining in Wall Street," she said, appealing to those Democrats who think she's too soft on banks. "The Republicans want to give them more power and repeal Dodd-Frank. That's what we need to stop"

The Single-Payer Attack

Nobody thinks a Republican Congress is going to allow a system of single-payer health care. With huge majorities, a Democratic Congress in 2009 and 2010 couldn't even push a weak public health insurance option into Obamacare.

Yet single-payer has managed to become a major issue in the Democratic primary -- one that Clinton injected into it. It's difficult terrain for Clinton. Democratic primary voters are sympathetic to single-payer, and Sanders, who's happy to call himself a democratic socialist, eagerly embraces it.

The Clinton campaigns messaging on the issue has been muddled: While it insists that Clinton herself supports the goal of universal health care , Clinton has attacked universal health care from a conservative direction, warning it would require major tax hikes on the middle class without mentioning the cost savings that would come with the elimination of premiums and deductibles. Chelsea Clinton went the furthest, bizarrely claiming Sanders wants to end Medicare, Medicaid and other programs, while throwing "millions and millions" off their health insurance.

By Sunday night's debate, Clinton had honed her attack. This time, the thrust of her argument boiled down to: Obamacare is as good as we can do, and opening up the health care debate again risks losing what we have.

Even when the Democrats were in charge of the Congress, we couldnt get the votes for [a public option], Clinton said. We finally have a path to universal health care. Weve accomplished so much already. I dont want to see us start over again with a contentious debate.

Clinton said she wants to build on the Affordable Care Act and to improve it by decreasing out-of-pocket costs and capping the amount Americans spend on prescription drugs.

Two hours before the Democratic debate in Charleston, Sanders finally made good on his promise to release an updated single-payer proposal before the Iowa caucuses on Feb. 1. (He last released one in 2013.) His plan for federally administered health care would be funded by a 2.2 percent tax on all Americans -- which his campaign called a premium, not a tax -- a new 6.2 percent tax on businesses, and increased income and estate taxes on the wealthy.

Clinton suggested more than once that opening up the debate could backfire, a warning that Democrats shouldn't go too far.

"We have the Affordable Care Act. That is one of the greatest accomplishments of President Obama, of the Democratic Party , and of our country," she said. "To tear it up and start over again, pushing our country back into that kind of contentious debate, I think is the wrong direction."

Sanders countered that there are still 29 million uninsured Americans, while rejecting the charge that he wants to dismantle Obamacare. Were not going to tear up the Affordable Care Act. I helped write it, he said.

Before Sunday, Clinton and her team had suggested that Sanders was withholding his health care proposal to avoid the perception that it would raise taxes on the middle class. After he released his plan, her press secretary, Brian Fallon, said in a statement that Sanders is making [details] up as he goes along.

Sanders said on Sunday night that he hoped Clinton would acknowledge that, overall, his plan would save people money. "It's a Republican criticism," he said of the tax jab.

The Tax Attack

The conventional wisdom is that Sanders (and the specter of Sen. Elizabeth Warren ) has pulled Clinton in a more progressive direction. But health care isn't the only issue where Clinton is hitting Sanders from a conservative angle.

During Sunday's debate, Clinton hammered on her promise not to raise taxes on households making less than $250,000 a year, which might sound trivial, but reflects a profound split within the Democratic Party.

"I don't think we should be imposing new big programs that are going to raise middle-class families' taxes," Clinton said during the last Democratic primary debate in December, once again pulling from GOP rhetoric. "I don't think a middle-class tax should be a part of anybody's plans right now."

Republicans tend to talk about government as "imposing" itself, while Democrats talk about it in terms of benefits, social insurance or giving back. The pledge not to touch taxes under $250,000 handcuffs what could be done, and Clinton has gone after Sanders for his paid family and medical leave proposal, which, like the Democrats versions in the House and Senate , would institute a small payroll tax to fund the program. Clinton says shed tax the wealthy instead so the U.S. wouldnt be one of the only countries in the world that doesnt guarantee paid family and medical leave.

Sanders has criticized Clinton for her tax-the-wealthy approach to paid leave, pointing out that popular programs like Medicare and Social Security rely on a payroll tax and, as a result, people feel more investment in them, and they have thus survived GOP attacks.

The Gun Attack

On gun safety, Clinton's been coming at Sanders from a liberal direction, perhaps the only chance she has to do it. The pressure pushed Sanders to flip -- or at least add in a ton of nuance -- to his position on what liability the gun industry has.

"I have made it clear, based on Sen. Sanders' own record, that he has voted with the National Rifle Association, the gun lobby, numerous times," she said. Sanders replied Sunday night that he had a D- rating from the NRA.

Her campaign has pointed to Sanders votes to give gun manufacturers and dealers legal immunity from civil lawsuits and his votes against the Brady bill that instituted the federal background checks system in 1993 to suggest that hes out-of-step with Democratic voters on the issue. Sanders has responded to Clintons scrutiny of his gun control record by noting he is in favor of banning assault weapons and closing a loophole that allows firearms to be sold at gun shows without the purchaser undergoing a background check, even though he represents a state that has many gun enthusiasts and few gun control measures.

I think Secretary Clinton knows that what she says is very disingenuous, he said in response to her attacks.

But Sanders didnt have a comeback when Clinton listed off his past votes that aligned with the NRA, including his vote for the so-called Charleston loophole, which allows gun sales to proceed after three days even if a background check has not been completed. As the candidates pointed out, the debate was held at a venue just a block from the Emanuel African Methodist Episcopal Church, where nine church members were shot last June by a man who purchased his weapon while his background check was still pending.

Clintons attacks have proved successful, as Sanders has just in the past few days worked to shore up his vulnerabilities on gun control. On Friday, Sanders said he would support legislation proposed by Rep. Adam Schiff (D-Calif.) and Sen. Richard Blumenthal (D-Conn.) that would repeal portions of the immunity law, leading to accusations from Clintons campaign that he was flip-flopping on the issue. And on Sunday, he said that he would take a look at closing the Charleston loophole.

The Obama Attack

In the middle of Sunday's debate, the Clinton campaign highlighted a major, if unsurprising, endorsement, and its framing told you everything about Clinton's strategy in South Carolina.

South Carolina was added to the early state primary calendar, along with Nevada, to offset the extreme lack of diversity in Iowa and New Hampshire, which have outsized abilities to influence the race. With South Carolina, the Democratic National Committee and state Democratic leaders intended to give the state's large black community a say in the debate, a move former DNC head Howard Dean talks about in a new interview.

Clinton, meanwhile, has looked to those voters as her firewall if she loses the first two states. With Obama still highly popular in the black community, Clinton clung Sunday night as closely to the president as she could, and didn't miss an opportunity to note that Sanders has been awfully critical of him in the past.

How fire-resistant that wall is remains to be seen. Rep. Jim Clyburn, the dominant figure in Democratic politics in South Carolina, said in the spin room after the debate that Obama was in the single digits in South Carolina before he won Iowa. If its perceived that [Clinton is] being rejected by voters, it would be a problem here, he told reporters.

The Wall Street Attack. Wait, What?

Another area where Clinton is attempting to out-progressive Sanders is, perhaps surprisingly, on Wall Street reform. Earlier this month, before Sanders was to give a speech on financial policy, Clintons chief financial officer issued a pre-emptive statement arguing that Sanders was being soft on Wall Street by taking a hands-off approach to regulating shadow banking , a broad term for various types of financial activities that aren't regulated as strictly as conventional lending.

Sanders wants to reinstate Glass-Steagall, the Depression-era banking legislation President Bill Clinton repealed that prevented big banks from engaging in both investment and commercial activities. Clinton has advocated for an approach that would more stringently regulate shadow-banking, but not break up the big banks.

Sanders campaign unveiled a new television ad Thursday that, for the first time, contrasted his record with Clintons. Since she gave him an opening by going after him on Wall Street reform, he points out that she has taken millions from big banks but is promising to tell them what to do. Clintons team immediately characterized the ad as a critical one that broke his promise not to run negative spots -- a complaint that signaled the Clinton camp was looking to go negative soon itself.

For Clinton, every attack on Sanders comes with a price: His backers shell out more small-dollar donations every time she hits him, with his campaign seeing a big uptick after it sent out a fundraising email arguing that Clinton was making vicious and coordinated attacks on his health care plan.

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