Our public spaces face an unacceptable terrorist threat. Though terrorism-related casualties are comparatively low, their cumulative impact is corrosive to the public happiness.

And the corrosion is growing.

Manchester, London, San Bernardino and Orlando.

Islamic State has inspired a toxic but potent rise of terrorism. It's a terrorism that sees streets not symbols and gatherings, not government offices, as its primary targets.

Fortunately, we are in a somewhat better position than are our European allies. People who go to large and medium-size public events in this country are nearly always screened with metal detectors. Event-goers can also expect their bags to be opened and inspected at the entry point.

The United States is also a harder place for terrorist recruiting. Our culture of assimilating immigrants isn't as consistently seen in Europe and is close to non-existent in some places. By including Muslim immigrants in the life of the nation, America reduces radicalization. Birthright citizenship, which some conservatives question, is actually one of the strongest tools for giving Muslim immigrants a stake in their new country's future. It also guarantees a stronger allegiance to Uncle Sam than Muslims in, say, France feel toward their adopted homeland.

This allegiance has been critical in snuffing out a considerable share of the failed terrorist plots since 9/11. A 2011 report by Duke University estimated that between 2001 and 2010, voluntary tips from Muslims loyal to America were decisive in thwarting at least 48 (and possibly as many as two dozen more) Islamic terror plots out of 161.

There is still plenty to do to secure our public places, which terrorists see as "soft targets." This effort shouldn't involve trampling constitutional liberties, but it will require discarding politically correct pieties.

Congress should pass legislation to provide legal authority for more effective screening measures at public events. These measures would center on a variation of the Israeli model for detecting terrorist attackers.

The legislation would have four interdependent components.

First, it would authorize government screeners at public events to use the sort of risk profiling Israel uses, which includes assessing demeanor, actions, clothing, situation (alone or with others), race, and religion in determining whether to screen an individual. These factors should not be viewed independently. A 2015 George Washington University study recorded that 40 percent of Americans arrested who had links to Islamic terrorism were converts to Islam. We cannot spot possible terrorists simply on the basis of their appearance.

Second, while taking into account such taboo considerations as race and religion, the legislation will guard against naked discrimination. It would not allow one assessed factor to justify a screening interaction unless supported by two associated factors. This would ensure officials consider the totality of circumstances before an interaction. The legislation would be narrowly tailored to a compelling government interest, namely preventing terrorist attacks. New police powers would bring with them new responsibilities. The federal government would be required to monitor abuses. Also, Washington should collect and study data to see which methods work best while constantly trying to modernize, improve and adapt methods so as to minimize intrusions and false positives.

Third, absent misconduct, the legislation would protect screening authorities from tort and other legal actions. Lacking a comprehensive legal framework for effective screening, local authorities currently defer to the advice of their attorney. Understandably concerned about the prospect of litigation, however, many legal advisers strongly recommend against any consideration of religion or race — even in the context of other factors. We must consolidate screening authorities to take necessary action.

Fourth, the legislation would mandate federal agencies to integrate this screening process into their broader counter-terrorism efforts. It would also redirect federal counter-terrorism grants to the provision of screening-training for local and state authorities. When it comes to screening, quality is more important than quantity. This training would be expensive. But money could be found by shuttering the Department of Homeland Security, which we have proposed before.

Ultimately, this legislation would address a simple imperative.

It would allow government to catch up with a present threat. It would do so by embracing a practical and proven strategy. The alternative wouldn't merely leave the public needlessly vulnerable, but would also, by so doing, stoke popular demand for harsh incursions into civil liberties. In Britain, terrorist attacks in 2005 ushered in a network of surveillance cameras. The next step could be facial recognition technology in which Big Brother can watch all citizens in all public spaces.

The London Bridge attack reminded us that terrorists have moved into a new era. It's time for America counter-terrorism law to do the same.