Candidates Donald Trump (l) and Jeb Bush participate in the Republican presidential debate at the Ronald Reagan Presidential Library. (AFP/Frederic J. Brown/Getty Images)

On Wednesday night, Republican presidential candidates met in Simi Valley, Calif., for their second debate. They touched on a remarkable variety of global issues, but despite the global ambition of the candidates, they barely mentioned one issue being discussed around the world.

This issue affects more than 50 million people directly, and perhaps billions indirectly – and it's an issue in which America is fundamentally intertwined, no matter how it may seem.

The global refugee crisis.

Yes, despite the photographs and headlines from Europe and the Middle East that have led newspapers and television news reports for weeks, the candidates were not asked about and barely mentioned refugees or migrants at all.

Refugees were brought up twice during three hours, albeit briefly. From the transcript, here's host Hugh Hewitt asking candidate Donald Trump a question that references Syrian refugees:

HEWITT: Mr. Trump, two years ago, President Obama drew a red line that the Syrian dictator Bashar Assad crossed, President Obama threatened to strike. He did not, his knees buckled.

We now have 4 million refugees, Syria is a living hell, and he turned to the Congress for the authority to back him up. You have three senators to your right that said, no. Do they bear responsibility for this refugee crisis, and what would you have done when Bashar Assad crossed the line?

TRUMP: I wouldn't have drawn the line, but once he drew it, he had no choice but to go across. They do bear some responsibility, but I think he probably didn't do it, not for that reason.

Somehow, he just doesn't have courage. There is something missing from our president. Had he crossed the line and really gone in with force, done something to Assad -- if he had gone in with tremendous force, you wouldn't have millions of people displaced all over the world.

As you can see, this is more an exchange about President Obama's "red line" in Syria and what many see as a missed opportunity for military intervention in the Syrian civil war. The people actually displaced from the war aren't given too much attention here at all.

The only other mention of refugees in the entire debate was made by candidate Rand Paul. Arguing against putting American boots on the round in Syria in the future, Paul said:

PAUL: My goodness, I'm still upset with the Saudi Arabians for everything they do over there. They've funded the arms that went to the jihadists. They're not accepting any of the people, any of the migrants that have been -- the refugees that are being pushed out of Syria. Saudi Arabia is not accepting one.

Again, Rand's comments here are being made in the context of American military action in the Middle East. He chooses to criticize the Saudi government's inaction in the refugee crisis. He certainly has a point: As WorldViews has pointed out before, Saudi Arabia and other wealthy Arab states have not resettled any Syrian refugees since the crisis began. The Saudi Arabian government has hit back at these charges, however, claiming it took in at least 100,000 Syrians but has not classified them as refugees.

What no-one talked about was whether the United States was pulling its weight in the refugee crisis. Following criticism from humanitarian organizations, the Obama administration recently raised the number of Syrians refugees it hoped to take in this year to at least 10,000.

However, a number of prominent groups have said that these numbers are still far too small and have asked for more than 100,000. “This 10,000 is basically the number we could do in our sleep,” Paul O’Brien, Oxfam America’s vice president for policy and campaigns said.

In the past, Republican presidential candidates have given a variety of answers when pressed on America's role in the refugee crisis. Some, such as Trump and Sen. Lindsey Graham (S.C.), have made vague statements in support of the United States accepting more refugees. Others, however, have pushed the other way: Louisiana Gov. Bobby Jindal said the idea was "ridiculous," while Carly Fiorina said the United States has already done its "fair share." A common theme among Republican candidates is concern about the potential security risks posed by Syrian refugees.

These security risks help explain why refugees from Syria and other parts of the Middle East hoping to stay in the United States often face long waits to find out if their cases have been accepted. Nadeen Aljijakli, a Cleveland-based immigration lawyer, recently told The Washington Post that her Syrian clients can end up in limbo. “If we don’t get an interview within six weeks, that means it’s probably gone to the black hole,” she said.

While there was barely a mention of refugees in the GOP debate, immigration was a frequent and notable topic. The words "immigrant," "immigrants" or "immigration" were used during the debate 36 times, and "migrants" was used once – by Paul when he meant to refer to refugees.

More on WorldViews

No, that viral image doesn’t show an Islamic State fighter among Europe’s refugees

The faces of Syrian children who only know life in a refugee camp