So far in the referendum campaign, Britain -- although traumatized by the brutal murder of British lawmaker Jo Cox -- has fortunately only been a spectator to the terrorist scourge of radical Islam. In Paris the brutal stabbing of a police officer and his partner (also a policewoman) in their house left their three-year-old son orphaned. Terrible enough, but the knife-wielding attacker also broadcast his actions live.
As Europe awoke to this new level of terror -- the potential of mass execution being streamed live -- the U.S. was experiencing its own horror with dozens slaughtered in the Orlando club shooting.
The Leave campaign barely missed a beat, warning Brits in a tweet that an Orlando-style massacre could be coming their way if they remain part of the EU. There were complaints of bad taste and the offending tweet was quickly taken down. Hours later it was back.
Security is just one of four main topics of the fractious debate; immigration, sovereignty, and the economy have also been (far richer) battlegrounds for each side.
In the early days the Remain campaign scored on the economy, dubbed by Leave supporters as "lies" and "scare tactics." The Remain team argued that the UK would be poorer alone, and gained ground. Leave has won big on immigration and to some degree sovereignty.
On security, the logic of each side is often reduced to the simplest argument. For the Leave campaign, controlling immigration reduces the radical Islamist threat, and for Remain supporters the EU is an early warning system -- alerting us that terrorists are coming. But it is more complicated than that.
A month ago I talked with Pauline Neville-Jones, a former security minister in UK Prime Minister David Cameron's government, and she told me that Europe gives the UK a lot; that it is a security buffer. "We get DNA information about individuals, we get information about car registrations... we get personal data about people," she said.
Daily threat warnings
For Neville-Jones, and those who have done her job and see the daily threat warnings and security concerns stream across their desks, In is a no-brainer. UK Home Secretary Theresa May, in the past something of a Euro skeptic, has come down on the side of Remain. Every day her top concern is getting the nation back to bed safely without a terror attack.
Many former British intelligence and military chiefs, like ex-MI6 boss Sir John Sawers and former MI5 chief Jonathan Evans, have lined up to agree with Neville-Jones and May.
But not all. Sir Richard Dearlove who once ran MI6 claims that Britain's open borders policy with the EU is against the country's interest. Others have made the point that the data sharing would continue, and bilateral interests would prevail over any loss suffered from withdrawing from Europol. Leave campaigners argue that Interpol's database is larger and more easily accessible than Europol's.
In recent weeks the London-based counter-terrorism think tank, the Quilliam Foundation, canvased 20 former security chiefs
and experts and found there was no clear consensus that put the either Leave or Remain security arguments significantly ahead of the other.
But the security arguments don't stop at terrorism. David Cameron raised the specter of UK exit potentially leading to a Europe-wide war,
invoking this country's great losses in the past.
"The serried rows of white headstones in lovingly-tended Commonwealth war cemeteries stand as silent testament to the price that this country has paid to help restore peace and order in Europe," he said. Cameron was criticized for using fear tactics.
European defense policy
His point, however, was not lost. The precursor to the EU was set up in the aftermath of two world wars to bind Europe's nations together and make such war impossible.
Still, arguments like this one, that on the surface should have seem so simple to win, have been wide of the mark and even backfired.
Boris Johnson, the often rambunctious former mayor of London and leading advocate in the Leave camp, has struck his target more often.
"What worries me now is that it's the European Union's pretensions to run a foreign policy and a defense policy that risk undermining NATO," he said.
He plays on the fear Britain will lose control, lose sovereignty of its armed forces, and that strikes a deep chord of national pride.
Johnson continued: "If we leave on June 23, we can still provide leadership in so many areas. We can help lead the discussions on security, on counter-terrorism, on foreign and defense policy, as we always have."
Obama urges UK to remain in EU
President Obama strongly disagrees
. It is the United States that struggled hard to help bring peace to post World War Europe, pushing the former foes to economic union. So it's no surprise that when he went to London in April this year he stood shoulder to shoulder with Cameron telling the British to vote Remain. As then, America today needs a united Europe, a strong NATO in the face of a resurgent, nationalist Russia.
But the big picture argument pales next to terrorism for most voters. The threat they can see, radical gunmen and bombers, is far more immediate than the insidious rise of nationalism and the big bear over the horizon.
They may be right to worry. Former spy Aimen Dean
spent years burrowed deep inside al Qaeda, leaking its darkest secrets and strategy to Western capitals. That ISIS has a leadership mandated strike surge now, during the Muslim holy month of Ramadan, is a worry in itself. But in Abu Dhabi last month he said: "They [ISIS] believe in the long run the strategic goal is to break up the body of the European Union that they perceive to be a formidable enemy."
And ISIS, he told us, understands well the fragility of the debate and the knife edge the vote is on. "A strike against the UK at this particular time is designed to influence the vote. If they can claim afterwards they were a decisive factor in the UK voters deciding to leave the EU and as a result break up the EU then they would claim it."
The stakes in this debate remain incredibly high. With the vote teetering on a knife edge -- potentially, even at this late stage, a victim to the ill winds of terrorism -- whoever wins the security debate may well win the overall referendum.