Sanctuary policies pose a threat to public safety, Sen. Pat Toomey (R., Pa.) thinks; his new legislation would block them from receiving some federal funds to try to change their minds.

"We've historically relied on common sense and a common sense of duty to protect the public from dangerous criminals," Toomey told the Washington Free Beacon in an interview Wednesday. "Unfortunately, that expectation no longer applies to these cities. So, we've got a bill that would withhold funding that the cities very much like, with the hope that that would begin to change their mind."

Toomey's bill, reintroduced last Thursday, would deny federal grant money to sanctuary jurisdictions, either cities or states. Toomey floated the proposal last year, when it was denied cloture as part of a series of votes on immigration taken by the Senate in a single whirlwind session.

The goal of the proposal, Toomey explained, is to "create a powerful disincentive so that the sanctuary cities would no longer be sanctuary cities." In his view, sanctuary policies endanger the public by permitting illegally resident offenders to roam the streets, rather than deporting them to their home countries.

Immigration enforcement is a federal responsibility, overseen by a bevy of agencies mostly under the umbrella of the Department of Homeland Security. Under federal law, however, immigration officials can delegate their enforcement authority temporarily to state and local law enforcement, permitting them to help with deportation. Federal officers can also issue detainers, asking local law enforcement to hold on to and eventually hand over individuals whom they have already arrested and subsequently ascertained to be illegally resident.

Sanctuary jurisdictions are those cities and states which refuse to coordinate with federal law enforcement on these immigration functions. An estimated eight states, as well as dozens of cities, fit the bill. Those include a number of counties in Toomey's state of Pennsylvania, as well as the largest city, Philadelphia. (Second-largest city Pittsburgh is not officially a sanctuary city, although Mayor Bill Peduto (D.) has signaled sympathy to the idea.)

"Pennsylvania has seen what happens with sanctuary cities," Toomey said. "They become a magnet for dangerous criminals who are in this country illegally."

He argued that illegally resident criminals flock to sanctuary jurisdictions because they know that if they are apprehended, they will not face deportation—that in a sense, city or state officials are on their side in a way that they would not be in non-sanctuary cities or states.

"Why in the world do they want to protect these people when among them are violent criminals?" Toomey said. "That's what we're talking about here: We're talking about people who are being picked up by local law enforcement for a reason. … The idea that we've got to protect these criminals from the consequences of their own prior criminal acts is just unbelievable to me."

Sanctuary jurisdictions have been a subject of debate in Pennsylvania, pitting the state's Republican-controlled legislature against liberal areas like Philadelphia. State legislators floated a bill last year to withhold funds from sanctuary cities in the state; the proposal was subsequently amended to make the cities legally liable for any individuals "adversely affected" by their failure to enforce federal immigration laws.

Such individuals would include the victim of Juan Ramon Vasquez, an illegal immigrant detained and then released by the Philadelphia police who subsequently sexually assaulted a five-year-old girl.

"It wasn't the police department's choice in the matter, it was what the politicians in Philadelphia forced on them. So they had to just release this guy back on to the streets, and a short time later he raped a young girl," Toomey said. "I mean that's just how horrendous this can be. This is not just a hypothetical; this has actually happened in Philadelphia."

Importantly, some conservative-leaning Pennsylvania counties are also ignoring immigration detainers. This is not out of principled opposition, but legal cautiousness—they fear that if their officers accidentally enforce an immigration detainer against the wrong person, they, rather than the federal government, would be held liable.

This caution is in response to recent court rulings which suggest cities and states can be held liable. Toomey—who said he does not "entirely agree with" the rulings—therefore also included language in his bill to make sure that the federal government would be liable in such circumstances.

"And that's the way it should work," he explained, "because in this context, the local police are really effectively being deputized by federal immigration officials, for a very brief period of time, until the feds can come and make the apprehension."

Although Toomey is focused on sanctuary policy, there is clearly a much larger immigration debate brewing in Washington. The border crisis continues to boil over with few fixes in sight, while the White House simultaneously pushes for merit-based immigration reform. Toomey did not give that proposal a full-throated endorsement; while "there are constructive elements in it," he believes that both high- and low-skilled immigration is needed, and that "we can welcome far more people that come to this country as legal immigrants."

While Toomey was not for the more restrictionist proposals of his Republican caucus colleagues, he was against something else more: Democrats' leniency on illegal immigration. When asked about this bigger picture, Toomey said that the Senate needs to find a "consensus," but thinks that will be hard, given the attitude of Senate Democrats.

"When our Democratic colleagues think that violent criminals should be allowed to stay and wander our streets freely without federal authorities being able to deport them, it's a little difficult to find common ground," he said.