House Homeland Security Committee Chairman Rep. Mike McCaul, R-Texas, called for the U.S. to temporarily suspend  the entrance of all Syrian refugees to the U.S. (AP Photo/J. Scott Applewhite, File)

A chorus of leading Republicans and one Democrat in Congress are calling for a halt on Syrian refugee admissions in the wake of the Paris terror attacks.

The list includes the Senate and House intelligence committee chiefs, the chairmen of the Senate Foreign Relations and Armed Services Committees, and chairman of the House Homeland Security Committee Michael McCaul (R-Texas), who today sent a letter to President Obama, demanding he suspend plans to take in Syrians fleeing conflict in their country.

“I call on you to temporarily suspend the admission of all additional Syrian refugees into the United States pending a full review of the Syrian refugee resettlement program,” McCaul wrote in a letter to President Obama Monday, in what is only the latest condemnation of the program.

“In this particular case, the high-threat environment demands that we move forward with greater caution in order to protect the American people and to prevent terrorists from reaching our shores.”

Reports that at least one of the perpetrators of Friday’s fatal bombing and shooting attacks entered Europe as part of the refugee flood fleeing war in Syria have set many lawmakers on edge. They worry that if one terrorist could slip through the cracks in Europe, terrorists could easily enter the United States as refugees too.

“There’s no possible way to screen them. It should be stopped immediately,” House Permanent Select Committee on Intelligence Chairman Devin Nunes (R-Calif.) said on “Face the Nation” Sunday.

“The Syrian refugee program should be suspended until the American people are satisfied that they know exactly who the President is admitting into the country via this program,” Senate Intelligence Committee Chairman Richard Burr (R-N.C.) said in a statement Monday. “There is simply too much at stake and the security of the American people should be our top priority.”

President Obama shot back at calls to close the country’s doors, arguing Monday that the U.S. didn’t have to turn away people in need to keep the this country safe.

“Slamming the door in their faces would be a betrayal of our values,” Obama said, speaking at the G-20 in Turkey. “Our nations can welcome refugees who are desperately seeking safety and ensure our own security. We can and must do both.”

[Raids spread across France and Belgium amid manhunt for suspects]

With Republicans in control of Congress, and pressure mounting from GOP presidential candidates — three of whom are senators — it is possible some of these efforts could gain traction. There aren’t many legislative workdays remaining before the end of the year, but lawmakers could try to attach language to a must-pass spending bill being considered in December.

But Democrats are unlikely to support that tactic and Obama might well issue a veto threat if such language were included. Some Republicans could also balk at tying the entire spending bill to a refugee-focused rider.

One powerful dissenting GOP voice emerged Monday in Sen. Ron Johnson (R-Wis.), chairman of the Senate Homeland Security and Government Affairs Committee, who said he did not support a blanket halt to refugee processing.

Instead, he said, a more rigorous “prioritization” of refugees be conducted to allow those who are at lower risk of radicalization — women, children and relatives of Syrian immigrants already in the U.S. — to proceed.

“I’m a lone wolf on this one, I guess,” Johnson said.

And at least one Democrat is publicly calling for Obama to prevent the entry of Syrian refugees.

Democratic Sen. Joe Manchin sent a letter to Obama on Monday along with his West Virginia colleague, Republican Shelley Moore Capito, calling for Syrian refugees to be kept out of the country until “the U.S. government can guarantee, with 100 percent assurance, that they are not members, supporters, or sympathizers of the so-called Islamic State of Iraq and Syria (ISIS), also known as Daesh or ISIL.”

The reaction of Republican lawmakers is hardly a knee-jerk response to the Paris attacks. Tensions over Syrian refugee admissions have been building in Congress over several weeks.

Since Obama first announced in September that the U.S. would take in at least 10,000 Syrian refugees – a fraction of the over four million who have fled war and the Islamic State  – congressional opponents have been drafting potential legislation bar the door.

McCaul released a bill in September, called the Refugee Resettlement Oversight and Security Act, that gives Congress the right to dictate the number of refugees allowed into the U.S. annually, effectively establishing a referendum on Obama’s plans to expand the refugee program. It would also require the Department of Homeland Security, the Director of National Intelligence and the Federal Bureau of Investigations to sign off on admissions.

McCaul’s measure already has the backing of Nunes and Armed Services Committee Chairman Mac Thornberry (R-Texas); on Monday, McCaul circulated a “Dear Colleague” letter to revive interest in the measure.

In the Senate, Judiciary Committee Chairman Chuck Grassley (R-Iowa) and Immigration subcommittee Chairman Sen. Jeff Sessions (R-Ala.) have appealed to appropriators to stymie Obama’s plan to accept Syrian refugees through the power of the purse.

“Not one dollar should be expended until stringent parameters for vetting these refugees are established,” Grassley wrote in a Nov. 4 letter to committee chiefs, pressing them to require administration provide pre-certification from intelligence and counter-terrorism officials before allowing Syrian refugees to enter.

Appropriators have yet to respond to Grassley’s request, even in the wake of the Paris terror attacks.

Sessions’ Monday letter to appropriators charged that the current refugee policy would increase the national debt and “will amount to a blank check to President Obama to carry out his entire refugee resettlement plan.” In his letter, Sessions proposed language to withhold money to settle refugees until Congress has specifically unlocked funding to do so every fiscal year, found costs and offsets, and identified refugees and recipients of asylum found to have a link to terrorism.

[Republican governors rush to slam doors on refugees]

Rep. Richard Hudson (R-N.C.) is expected to also introduce a bill to require DHS, the DNI, the FBI director, and the attorney general to vouch to Congress that every refugee is not a security threat. That would effectively serve as another moratorium on the president’s plans, as in the last several weeks, even administration officials admit they cannot have complete information about every refugee applying to come to the U.S.

“They are rolling the dice here,” Rep. Peter King (R-N.Y.) complained about the administration’s vetting standards on “Fox News Sunday.” “We know that ISIS wants to bring in terrorists with these refugees…unless they can show 100 percent that a person is not involved with ISIS, because right now, there’s no responsible way to do the vetting. That’s the reality.”

But even in the wake of a terrorist attack that has caused near-universal revulsion in the West, Republicans may have a hard time stopping Syrians from arriving here.

Democrats are backing up the president by slamming those who would seal U.S. borders to Syrians.

“To turn our backs on those escaping persecution, many of them religious minorities, runs counter to the proud and generous heritage of a United States that has always helped those in need during turbulent times,” said Rep. Adam Schiff (D-Calif.), ranking member on the House Permanent Select Committee on Intelligence.

“There is a balance to be struck here between ensuring that we carry our part of the burden of welcoming refugees from around the world and making sure that we are ensuring that the safety and security of the American people,” said Sen. Chris Coons (D-Del.), a member of the Senate Foreign Relations Committee.

And not all Republicans think stopping Syrian immigration would keep the country any safer.

“There’s about 20 different ways of getting to America. Refugees are just one of 20 lanes — shutting that lane down does not protect us,” Sen. Lindsey Graham (R-S.C.), who is also a 2016 presidential candidate, said on CNN. “Yes, ISIL can intermingle among refugees, they are doing that, but there’s other ways of them getting here…shutting off refugees doesn’t destroy ISIL.”

Kelsey Snell and Mike DeBonis contributed to this report.