“Thirteen Syrian refugees were caught trying to get into the US through the southern border,” Trump wrote in a Nov. 22 Twitter post . “How many made it? WE NEED THE WALL!”

Leading Republican presidential candidate, the unapologetically bombastic real estate tycoon and TV personality Donald J. Trump has mostly framed the Syria issue in relation to his call to build a wall on the US-Mexican border to keep out illegal immigrants and, he claimed, deter potential IS militants who might pose as Syrian refugees to try to enter the United States. The Mexican government should pay for this wall, Trump has proposed.

With international talks on Syria set to resume at the United Nations in New York in the coming days, here are the leading US presidential candidates’ positions on Syria, combating the Islamic State (IS) and the admission of Syrian refugees to the United States.

Trump, 69, has called for speeding up the fight against IS, ideally using ground troops provided by other countries, backed up by the United States. But he did not specify who would be willing to provide such ground forces, and he has been vague about how he would speed up the fight. He also called for designating a “swatch of land” in Syria that could serve as a Syria safe zone that should primarily be funded, he said, by the Gulf states.

"We've got to get rid of [IS] quickly, quickly,” he told a campaign rally in Worcester, Massachusetts, on Nov. 18. “Let me tell you what I really want to do. I want to get other people to put troops on the ground and we'll back them up 100 percent.”

Trump proposed the idea of building “a safe zone in Syria; build a big, beautiful safe zone, and you have whatever it is, so they can live,” he told a Tennessee campaign rally on Nov. 16. “We give a little bit but other countries, like the Gulf states, should fund it,” he said.

On Dec. 7, Trump controversially called “for a total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what is going on,” his campaign said in an official press release. The position has been almost universally denounced by rival candidates — “unhinged,” Jeb Bush responded on Twitter; “disqualifying” for the presidency, said the White House — as well as by key allies abroad and the Pentagon as being detrimental to US national security. On Dec. 10, Trump canceled a planned post-Christmas trip to Israel after the office of Israeli Prime Minister Benjamin Netanyahu said he did not agree with Trump’s remarks about Muslims.

Dr. Ben Carson

Retired pediatric neurosurgeon and leading GOP presidential candidate Ben Carson has called for halting the admission of all Syrian refugees to the United States. He has also called for pursuing an end to the Syrian conflict by providing support to rebels battling Syrian President Bashar al-Assad and IS, backing a safe zone on the Turkish-Syrian border and for the United States to provide more help to frontline countries hosting millions of Syrian refugees, especially Jordan where he traveled in November to visit a Syrian refugee camp.

Given the Nov. 13 terrorist attacks in Paris, “The US simply cannot, should not and must not accept any Syrian refugees,” Carson wrote in Time magazine on Nov. 17, rejecting the Obama administration plan to permit additional Syrian refugees over the next two years.

“The reality is that the threat of radical Islam and the corrosive influence of Sharia law here in the US is not just a figment of our imagination,” Carson wrote. “The US must defend itself by preventing the infiltration of terrorists who pose as refugees to enter our land.”

“We must find a political end to this conflict,” Carson said in a campaign press release on his trip to visit a Syrian refugee camp in Jordan on Nov. 28.

“Millions of refugees have now been waiting years for the end of the war to come in Jordan, Lebanon and Turkey,” the Nov. 28 Carson campaign release said. “Until it is safe for them to return home, Jordan is a safe place for them to wait.”

“The United States must do more,” the Carson campaign statement said, but added, “We can do our part to help this crisis without bringing 10-25,000 refugees to the United States. Jordan already houses 1.4 million refugees. Jordan needs and deserves our logistical help and financial support.”

In an Oct. 7 interview with Breitbart News, Carson called for weakening both Assad and IS. The United States should “continue to assist Syrian insurgent forces in their conflict against pro-Assad and [IS] forces with advisers, intelligence and weapons,” Carson told Breitbart News. The United States should also work with NATO ally Turkey to establish a “no-fly/no-fire zone along the Turkish-Syrian border,” Breitbart said Carson proposed.

Sen. Marco Rubio

Florida Sen. Marco Rubio has cast himself as among the more hawkish candidates among his Republican rivals, supporting a Syria no-fly zone and saying he would consider sending US ground troops into the conflict. But it is worth noting Rubio, along with fellow Republican Senators and rival presidential candidates Ted Cruz (Texas) and Rand Paul (Kentucky), voted against authorizing US President Barack Obama to use force against Assad for using chemical weapons in September 2013. Rubio has also come out against allowing any Syrian refugees into the United States, after earlier saying he might be open to that.

“When I am president, what I will do to defeat [IS] is very simple: whatever it takes,” Rubio wrote in Politico Magazine Nov. 19. “Exactly what it will take will depend on how the situation on the ground changes over the next 15 months.”

“I would protect the homeland by immediately stopping the flow of Syrian refugees into the United States — not because refugees fleeing conflict are unwelcome, but because it is currently impossible to verify their identities or intentions,” Rubio, 44, wrote. “Next, I would reverse defense sequestration so we have the capabilities to go on the offense against [IS].”

Rubio said he would consider sending US ground forces as part of a multinational coalition to Iraq and Syria to aid local forces on the ground. He said he would declare a Syria no-fly zone to stem the flow of refugees and provide a place to train and arm Syrian rebel fighters.

Regarding Syrian refugees, Rubio, in the wake of the Paris terrorist attacks in November, said the United States can’t afford to let them in. "It’s not that we don’t want to," Rubio told ABC's "This Week” Nov. 15 about accepting Syrian refugees. "It’s that we can’t." Earlier, in September, Rubio said he would be open to letting some Syrian refugees come to the United States.

Sen. Ted Cruz

Texas Republican Sen. Ted Cruz has called for increasing US air operations targeting IS, arming the Kurds and ending the effort to arm Syria’s Arab rebels. Cruz, 44, has also called for legislation blocking admission to the United States for Syria’s Muslim refugees, while saying he would support the United States welcoming Christian refugees from the Middle East.

The “idea that we should bring tens of thousands of Syrian Muslim refugees to America … is nothing less than lunacy,” Cruz told Fox News Nov. 15. “On the other hand, Christians who are being targeted for genocide, for persecution … we should be providing safe haven to them.”

“We should stop engaging in the fiction of trying to find these moderate rebels and support them,” Cruz said in an interview with Fox News posted to his campaign website. “We should stop the fiction of trying to bring together the Sunnis and the [Shiites] to put down their arms and embrace like brothers."

He continued, “Instead we should defend US national security interests and do what works to defeat [IS]." Cruz added, “Now what would that mean? That’d mean number one, using overwhelming air power to target and destroy [IS]. Number two, we need to be arming the Kurds … they’re strong allies of America and yet the Obama administration refuses to fund them because it wants to send the weapons to Baghdad. … We need to focus on what works.”

Cruz, in September 2013, said he would vote against a congressional measure to endorse Obama’s plan to strike Syrian forces for using chemical weapons. (Obama ended up deciding not to carry out the strikes, making a deal with Russia’s Vladimir Putin to force Syria to give up its chemical weapons arsenal instead.)

“Just because Assad is a murderous thug does not mean that the rebels opposing him are necessarily better,” Cruz wrote in The Washington Post on Sept. 9, 2013.

Jeb Bush

Among Republican presidential candidates, former Florida Gov. Jeb Bush has offered one of the more detailed treatments of the issue of how to stabilize Syria as part of his larger set of policy objectives for how to combat IS. Among his proposals, Bush, 62, has called for establishing multiple safe zones and a no-fly zone in Syria, to protect Syrians not only from IS but also from Assad, and bolstering the training and support to moderate Syrian rebels fighting IS.

“Our ultimate goal in Syria is to defeat [IS] and to achieve long-term political stability in that country,” Bush said in an August speech at the Ronald Reagan Presidential Library. “Defeating [IS] requires defeating Assad, but we have to make sure that his regime is not replaced by something as bad or worse.”

To that end, Bush proposed a four-part plan, including leading a coordinated, international effort “to give Syria’s moderate forces the upper hand” and to expand and improve the recruitment and training of Syrian forces fighting IS. Bush said the United States “and our partners should declare a no-fly zone in Syria, and then work to expand that zone to prevent more crimes by the regime.”

Though his policy seems to have much in common with the Obama administration’s approach, Bush has criticized the Obama administration’s strategy of the war against IS as incremental and under-resourced and suffering from half measures.

“America will not be safe if we only play defense. Gov. Bush believes that in addition to bolstering our defenses at home, we must take the fight to the terrorists who have declared war on us and our way of life,” the Bush campaign said in a Dec. 9 press release. “Jeb Bush is the only candidate in the race who has outlined serious and substantive plans to destroy [IS], restore the American military and reverse President Obama’s risky counterterrorism policies.”

DEMOCRATIC PARTY

Hillary Clinton

Former US Secretary of State and Democratic front-runner Hillary Clinton has proposed using a combination of intense US-led international diplomacy, air power and special forces, support for local rebel forces and the Kurds, and a no-fly-zone to get a diplomatic solution on Syria as part of a comprehensive strategy to defeat IS, a challenge that she warns will take a long time.

Like Obama, Clinton opposes sending US ground forces to Syria, but supports his call to send more US special forces to Syria to help intensify the campaign and work with local forces combating Assad and IS. Beyond combating IS in its core base in Syria and Iraq, Clinton has proposed intensifying efforts to dismantle the “terrorist infrastructure” facilitating the flow of foreign fighters and financing to IS, as well as working with technology companies to combat IS’ ideology and online recruitment, which has resulted in as many as 31,000 foreign fighters joining the terrorist group.

“We need to move simultaneously toward a political solution to the civil war that paves the way for a new government with new leadership, and to encourage more Syrians to take on [IS] as well,” Clinton said in a speech to the Council on Foreign Relations (CFR) in New York on Nov. 19. “To support them, we should immediately deploy the special operations force President Obama has already authorized, and be prepared to deploy more as more Syrians get into the fight.”

“We should also work with the coalition and the neighbors to impose no-fly zones that will stop Assad from slaughtering civilians and the opposition from the air,” Clinton said. “Opposition forces on the ground with materiel support from the coalition could then help create safe areas where Syrians could remain in the country rather than fleeing toward Europe.”

“This combined approach would help enable the opposition to retake the remaining stretch of the Turkish border from [IS], choking off its supply lines,” Clinton said. “It would also give us new leverage in the diplomatic process that Secretary Kerry is pursuing.”

“Resolve means depriving jihadists of virtual territory just as we work to deprive them of actual territory,” Clinton said in a speech to the Brookings Saban Forum on Dec. 6. “They are using websites, social media, chat rooms, and other platforms to celebrate beheadings, recruit future terrorists, and call for attacks. We should work with host companies to shut them down.”

“Our goal is not to deter or contain [IS] but to defeat and destroy [IS],” Clinton told CFR. “But we have learned that we can score victories over terrorist leaders and networks only to face metastasizing threats down the road. So we also have to play and win the long game.”

“Our strategy should have three main elements,” Clinton said. “One, defeat [IS] in Syria, Iraq, and across the Middle East; two, disrupt and dismantle the growing terrorist infrastructure that facilitates the flow of fighters, financing arms, and propaganda around the world; three, harden our defenses and those of our allies against external and homegrown threats.

Clinton has said the United States should be vigilant in screening but must not close the door on Syrian refugees.

“We cannot allow terrorists to intimidate us into abandoning our values and our humanitarian obligations,” Clinton told CFR. “Turning away orphans, applying a religious test, discriminating against Muslims, slamming the door on every Syrian refugee — that is just not who we are. We are better than that.”

Bernie Sanders

Sen. Bernie Sanders, a Vermont Socialist who caucuses with the Democrats, has generally supported Obama’s approach of leading an international coalition to combat IS and trying to achieve a diplomatic resolution of the conflict. But Sanders has opposed sending US special forces or ground troops into Syria and has urged the United States to work in an international coalition with other nations to try to achieve a diplomatic settlement.

Sanders has opposed Republican calls to block admission of Syrian refugees to the United States. He has also opposed setting up a Syria no-fly zone, as his Democratic challenger Hillary Clinton and several Republican presidential candidates have advocated.

“I think that there's a lesson to be learned from Iraq and Afghanistan, [that] what a great military power like the United States is about is trying to use diplomacy before war and working with other countries rather than doing it alone,” Sanders told ABC’s “This Week” on Oct. 18. “At the end of the day, a military coalition is what will succeed, not the US doing it alone.”

Asked Nov. 8 if he opposed Obama’s call to send some 50 US ground forces to Syria, Sanders said he understood that Obama was trying to “thread a very difficult needle,” but worried the United States could incrementally get sucked into intervening in the Syrian conflict more deeply than he thought it should.

Obama is “trying to defeat [IS],” Sanders told ABC’s "This Week" on Nov. 8. “He's trying to get rid of this horrendous dictator, Assad. But at the same time, he doesn't want our troops stuck on the ground. And I agree with that. But I am maybe a little bit more conservative on this than he is. I worry that once we get sucked into this, once some of our troops get killed and once maybe a plane gets shot down, that we send more in and more in. But I will say this. [IS] must be defeated primarily by the Muslim nations in that region. America can't do it all. And we need an international coalition. Russia should be part of it — UK, France, the entire world — supporting Muslim troops on the ground, fighting for the soul of Islam and defeating this terrible [IS] organization."

Following the terrorist attacks in Paris on Nov. 13, Sanders said he supported Obama’s efforts to lead an international coalition to combat IS. Sanders, like Clinton and fellow Democratic presidential candidate Martin O’Malley, also strongly rejected Republican calls to block the admission of Syrian refugees, as well as what he called growing “Islamophobia” promoted by some Republican candidates.

“Now is the time — as President Obama is trying to do — to unite the world in an organized campaign against [IS] that will eliminate the stain of [IS] from this world,” Sanders told a campaign rally in Cleveland on Nov. 16.

“What terrorism is about is trying to instill terror and fear into the hearts of people,” Sanders said. “And we will not let that happen. We will not be terrorized or live in fear. During these difficult times, we will not succumb to Islamophobia. We will not turn our backs on the refugees who are fleeing Syria and Afghanistan. We will do what we do best and that is be Americans — fighting racism, fighting xenophobia, fighting fear.”