In the wake of the Paris terror attacks - and amid continuing threats of violence in cities like Brussels - the 2016 presidential candidates have offered more details on their foreign policy plans in recent days. Here's a roundup of how the candidates say they'd handle the threat from the Islamic State of Iraq and Syria (ISIS), from the military campaign overseas to protecting the homeland.
Hillary Clinton: Clinton outlined her strategy to fight ISIS in a speech Thursday, calling for "more allied planes" and "more strikes" on the group's enclaves in Iraq and Syria.
"We have to fit a lot of pieces together, bring a lot of partners along, move on multiple fronts at once," the former secretary of state said during the speech. "But if we press forward on both sides of the border, in the air and on the ground, as well as diplomatically, I do believe we can crush ISIS's enclave of terror."
She said the U.S. needs to pass an updated Authorization for the Use of Military Force (AUMF), but said it would be a "mistake" to send in American combat troops, even if there is an attack on U.S. soil. Instead, she said she would work to persuade more Iraqi Sunnis to join the fight, arm them if necessary, and convince Turkey and Gulf countries like Saudi Arabia and Qatar to partner with the U.S.
She also advocated for a no-fly zone over northern Syria to protect civilians from the violence, but says the U.S. should admit refugees after background checks and intelligence gathering for the vetting process.
Martin O'Malley: Positioning himself in opposition to Clinton, the former Maryland governor said at the CBS News Democratic debate that "we do have a role in this."
The responsibility, O'Malley is "not solely ours, but we must work collaboratively with other nations."
The former Maryland governor has called for more U.S. investments in human intelligence and has criticized Clinton for not focusing on that issue. On ABC's "This Week" Sunday he argued for working through the U.N. Security Council to fight ISIS in the Middle East.
He also believes Congress should make it harder for people on terror watch lists to buy combat assault weapons in the United States.
He also believes that the U.S. should accept 65,000 Syrian refugees.
Bernie Sanders: The Vermont senator wants to build a global coalition to take on ISIS, saying in Iowa on Sunday that he would even be open to working with Russia and Iran to defeat the extremist group.
"Russia has got to join us. We are concerned about Iran, but Iran has to join us. We have concerns about Saudi Arabia, but Saudi Arabia has to join us," Sanders said in a speech delivered at Simpson College. "If all over the world these attacks are taking place, the world has got to come together."
He said in a foreign policy speech last week that the coalition should include Western powers, Muslim nations and countries like Russia. They should share counterterrorism intelligence, cut off ISIS' funding, and "end support for exporting radical ideologies."
He also specifically called on Gulf countries like Saudi Arabia, Kuwait and Qatar to play a larger role in the campaign against ISIS. In terms of the U.S. military role, Sanders said that military force should be "a last resort, not a first resort."
Donald Trump: Trump has come under fire in recent days for arguing that the U.S. should "strongly consider" shutting down mosques as the "common sense" solution to preventing terrorism in the U.S. He also faulted New York City Mayor Bill de Blasio for ending a program to gather information from mosques.
A day before the Paris attacks, the businessman said in Iowa that to destroy ISIS, he would "just bomb those suckers."
"I'd blow up the pipes, I'd blow up the refineries. Every single inch -- there would be nothing left," he told reporters. In the wake of attacks, he's kept up that recommendation.
Trump has also applauded Russia for attacks against ISIS. In September, when Russia launched its first air strikes over Syria, Trump said of Vladimir Putin: "If he wants to fight ISIS, let him fight ISIS. Why do we always have to do everything?"
He has promised to deport all Syrian refugees who resettle in the U.S. if he is elected president.
Ben Carson: Retired neurosurgeon Ben Carson is open to using "every resource available to us" when it comes to defeating ISIS.
On Monday after the deadly events in Paris, Carson said, "we ought to take this as a warning that we need to really go in there with very serious intent not to contain them, but to take them out completely."
"To destroy them, to eliminate them, I would use every resource available to us," he said.
He believes the U.S. needs to help broker a cease-fire in Syria, in part by forming a coalition government there.
Carson has come under fire for likening Syrian refugees to "rabid dogs" and saying the U.S. needs to maintain a "database" of every person entering the United States. He has also said mosques should be subject to increased scrutiny if they are encouraging terrorist activities.
Jeb Bush: In a speech at a South Carolina military college last week, the former Florida governor said the U.S. also needs to put boots on the ground in Syria and Iraq. He said he would leave the exact number of troops up to the military commanders, but said in general, his administration would call for an increase of 40,000 active-duty soldiers in the Army with a total force of 186,000 Marine Corps.
He would restore the National Security Agency's (NSA) powers under the Patriot Act's metadata program, which Congress voted to strip of certain abilities earlier this year with the USA Freedom Act.
"If there was ever a time for such a program, it's now, and yet too few in Congress were courageous enough to defend this program when it mattered most," he said.
He also believes the U.S. should enforce a no-fly zone in Syria to give refugees a safe haven there, although he has advocated for special treatment for Christian Syrians.
Marco Rubio: Florida Sen. Marco Rubio, prior to the Paris attacks, agreed with the president's decision to send about 50 special forces to Syria. He told CBS' "Face the Nation" in early November that it was an "important start" to defeating ISIS, but he also believes that the war called for an increase in the number of Special Forces in the war-torn country.
In an interview with CBS News Chief White House Correspondent Major Garrett, Rubio said that the U.S. "will need a significant number of special operators" to supplement a majority Sunni ground force.
"Ultimately, we would want to know what the outcome is -- that a combined Sunni force on the ground - made up of Sunni fighters from Egypt and Jordan and Saudi Arabia and Sunnis from Iraq and Syria - defeat ISIS militarily and ideologically," Rubio told Garrett. "That is the end goal. That will not happen unless the United States provides the air support, the logistical support and embeds alongside them a significant number of special operations forces along with our coalition partners doing their part in each of these endeavors as well."
In an op-ed in Politico published last week, he said the U.S. should shut off the flow of Syrian refugees to the United States by enforcing no-fly zones in Syria, ending limits on overseas data collection, restoring the NSA's data collection powers and reversing mandatory defense spending cuts. He also advocated for a multinational coalition of countries to send troops into Syria and said he would demand that Iraq's Shia Muslim government give greater autonomy to Sunnis.
At home, Rubio has also said suggested that the U.S. shut down any institution "where radicals are being inspired."
Lindsey Graham: The South Carolina senator plans to introduce a bill after the Thanksgiving holiday that would authorize the use of military force in the fight against ISIS -- without time limits or geographic boundaries. If members of Congress "aren't willing to declare war on ISIL," he says, they are "making a mistake for the ages."
The AUMF would allow "this president and every future president the ability to go anywhere ISIL goes, use any means necessary," according to Graham, who used an alternate acronym for the group.
He has consistently said the U.S. should send 10,000 troops into the region to fight ISIS.
Ted Cruz: Asked earlier this month whether he would support American boots on the ground, the Texas senator said in Iowa: "We have boots on the ground. The Kurds are our boots on the ground."
Instead, Cruz has called on Congress to pass the Expatriate Terrorist Act, a bill he introduced last year that would allow government officials to take away U.S. citizenship for anyone suspected of supporting terror groups.
He also believes the president must formally declare war against the group, according to the Constitution.
Cruz has also said that the U.S. should reject any Muslim refugees from Syria but allow Christians in, because "there is no meaningful risk of Christians committing acts of terror."
John Kasich: In an interview with CBS News Chief White House correspondent Major Garrett the Ohio governor and Republican presidential candidate called for a worldwide coalition -- including NATO countries along with other Middle East nations -- to become involved in fighting ISIS.
"I would say no fly-zones. I would say arm the Kurds who are taking the fight to ISIS in Iraq and put a coalition together to get both in the air and on the ground to destroy ISIS," Kasich said. "And it's got to be a broad-based coalition but it has to mean action. Ultimately we destroy ISIS, and we're going to see a significant improvement in the ability of America to assume a leadership role again."
Rand Paul: The Kentucky senator published an op-ed published last week in Time, calling for the U.S. to take a "hard look at what is fueling [ISIS] growth: money."
He called for governments and private sources to begin policing funding for the extremist group -- particularly those based in Saudi Arabia, Qatar, and Kuwait.
"From now on, our message to these governments and their ruling families must be clear: take accountability for your role in murdering our citizens or we will freeze your assets," Paul wrote in his editorial. "Locate the citizens who are financing terrorism and lock them up or we won't sell you a single missile or fighter jet. The U.S. does not do business with terror financiers, period."
Paul has previously called for a declaration of war against ISIS and introduced a war resolution to Congress last year. He has argued that Russia should be part of a brokered cease-fire in Syria and that the boots on the ground fighting ISIS should come from Arab countries in order to ensure a lasting peace.
He introduced legislation proposing that the U.S. temporarily stop issuing visas to anyone coming from a country with a "high risk of terrorism" and impose a waiting period for background checks on visas from all other countries. He also advocates reforms to the visa waiver program to allow time for background checks.
Carly Fiorina: Former tech executive Carly Fiorina wants the U.S. to "wage a war" against ISIS. At a Republican event in Iowa Friday she expanded: "What we must do is deny ISIS territory and that means we must cut off their supply lines, we must cut off their money."
Rick Santorum: The former Pennsylvania senator has said that denying ISIS territory is key to defeating the terror group.
"Once ISIS established a caliphate, the game changed because once you establish a caliphate, you have an area of control, you have to take ground from that caliphate, because if you don't, then, in the Islamic world, it's seen as a legitimate caliphate," he said at the Republican undercard debate in September. He has said he would send in 10,000 U.S. troops and more if necessary.