(CNN) Of the 4 million Syrian refugees who have fled attacks by their government and ISIS, the United States has taken in 0.03% of them.

That's a pitiful number that needs to be changed immediately, a growing number of Americans say. Both Republican presidential candidate Donald Trump and Democratic candidate Martin O'Malley agree: the U.S. needs to step up.

But how many should the United States take in? And what risks would be involved?

How the U.S. fares

So far, the U.S. has accepted 1,500 Syrian refugees. By contrast, Germany said it will take in 800,000 migrants in the current refugee crisis . Several other countries, such as Turkey, Jordan and Lebanon, have each taken in hundreds of thousands of Syrians.

The International Rescue Committee called for the United States to open its doors to 65,000 Syrian refugees.

An online petition asking the U.S. government to do exactly that has garnered more than 54,000 signatures

"The U.S. has historically been the world leader in recognizing the moral obligation to resettle refugees," International Rescue Committee president and CEO David Milliband said.

"But in the four years of the Syria crisis, there has been inertia rather than leadership."

What the government says

The Obama administration says is considering helping more with refugee resettlement. State Department spokesman John Kirby said he anticipates the figure of 1,500 accepted refugees to double before the end of the year.

"I expect to see the U.S. will take in even more going forward," Kirby told CNN last week.

The National Security Council said the United States has helped quite a bit financially.

"It is important to note that the United States has provided over $4 billion in humanitarian assistance since the Syrian crisis began, and over $1 billion in assistance this year," NSC spokesman Peter Boogaard said. "The U.S. is the single largest donor to the Syrian crisis."

Where's the hurdle

Some say opening the country to more Syrian refugees runs the risk of having extremists slip through.

Republican presidential candidate Marco Rubio, a son of immigrants, said the U.S. must be careful.

"We would be potentially open to the relocation of some of these individuals at some point in time to the United States," he said.

"We'd always be concerned that within the overwhelming number of the people seeking refugee, someone with a terrorist background could also sneak in."

But the process for Syrians seeking asylum in the United States is complicated by a long security vetting procedure meant to ensure that only desperate refugees -- not extremists -- reach American soil. It typically takes 18 months before a refugee designated for resettlement in the United States can actually set foot in the country.

Where opposing presidential candidates agree

GOP frontrunner Donald Trump, whose campaign often focuses on expelling illegal immigrants, said the United States should accept more Syrian refugees due to the " unbelievable humanitarian problem ."

"I hate the concept of it, but on a humanitarian basis, with what's happening, you have to," Trump told Fox News.

Democratic presidential candidate Martin O'Malley backed the IRC's call for the U.S. to accept 65,000 refugees.

"Americans are a generous and compassionate people," he said. "But today our policies are falling short of those values. We must do more to support Syrian refugees -- and we must certainly welcome more than the proposed 5,000 to 8,000 refugees next year."

New Jersey Gov. Chris Christie said Obama hasn't acted strongly enough during the Syrian crisis and "has allowed these folks to be slaughtered."

"I frankly can't imagine as president of the United States how you could permit this to happen on this scale," he said. "And now we're seeing those results."

Democratic presidential candidate Hillary Clinton, who was secretary of state when the Syrian crisis unfolded, said she and other members of the Obama administration wanted to be more aggressive helping Syrian rebels in their battle against Syrian President Bashar al-Assad's regime.

"I advocated for a more robust policy," Clinton told MSNBC. She said she called on the "entire world" to come together to solve the crisis.

But Michel Gabaudan, president of Refugees International, said the United States can't be blamed for extreme violence in Syria.

"To accuse Washington of the tremendous horrors that al-Assad has been vesting on his own people is perhaps going a step too far," he said.

What's in it for the United States

The United States also stands to gain from helping Syrian refugees, Gabaudan said.

"I would argue there is another obligation beyond a moral obligation to help refugees -- and to help particularly those who are in Turkey, in Lebanon and in Jordan," he said.

"These countries are allies of the U.S. We have a moral obligation to look after the refugees, but we also have an interest in the security of these countries, and that the refugees in these countries do not lead to some destabilization. And that's another factor why we should move further in providing assistance."