This article is from the archive of our partner National Journal

Last week, President Obama said that U.S. intelligence agencies have not detected any plots by Islamic State militants to stage an attack on U.S. soil. But some Republicans are worried that members of the terrorist group could still be headed this way—and they might cross into the country through the Mexico border.

The concern isn't new. In August, Texas Gov. Rick Perry said in a speech at the Heritage Foundation that "individuals from ISIS or other terrorist states could be" crossing into the U.S. through the Mexico border. Last week, at a congressional hearing on ISIS, Rep. Jeff Duncan, R-S.C., said that "with a porous southern border, we have no idea who's in our country." And on Wednesday, Rep. Bennie Thompson, D-Miss., asked Homeland Security Secretary Jeh Johnson whether the threat of ISIS coming in through Mexico is real.

"We see no specific intelligence or evidence to suggest at present that ISIL is attempting to infiltrate this country through our southern border,"  Johnson replied, using a different name for the terrorist group.

Other Homeland Security officials have echoed Johnson's assurances. "There is no credible intelligence to suggest that there is an active plot by ISIL to attempt to cross the southern border," the department said in a recent statement.

Administration officials are far more worried about ISIS militants entering the United States another way: on a flight from the Middle East, using American or European passports. The way terrorists attempt to infiltrate the country, counterterrorism officials say, hasn't changed since the Sept. 11 terrorist attacks, in which the perpetrators hijacked domestic flights they boarded as passengers.

"The numbers of known watchlisted individuals that we have encountered at the southern border is minimal compared to commercial flight," John Wagner, the U.S. Customs and Border Protection's assistant commissioner of the office of field operations, said at a congressional hearing last week.

Democrats say Republicans are playing on the fear of ISIS entering the U.S. through Mexico to point to the White House's immigration policy this year, especially ahead of the midterm elections. According to a Politico poll released Monday, 64 percent of voters in competitive House and Senate races say they disapprove of Obama's handling of immigration, while just 35 percent say they approve. By pulling ISIS into the immigration debate, Republicans are drawing attention to Obama's policy on border security, hoping to win voters who are already skeptical about the president's handling of the issue.

This article is from the archive of our partner National Journal.

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