I had a series of posts that I was planning to finalize starting today about the Brexit referendum but, of course, the news of Jo Cox’s murder has preempted everyone’s thoughts about the European Union debate today.

There will be plenty of time for more debate in the week ahead, one of the most important weeks of political debate in the United Kingdom’s postwar history and, indeed, in Europe’s postwar history.

But it will now be forever marred by Cox’s assassination, especially if, as has been widely reported, the gunman shouted out ‘Britain first!’ as he was shooting the 41-year-old Labour MP.

Cox, a wife who leaves behind a grieving husband, Brendan, and two young children, was elected to the House of Commons in 2015 after a longtime career with Oxfam and other charitable organizations. She was in particular passionate about providing relief to those suffering in war-torn Syria. As a Labour candidate and MP, she was a passionate supporter of  resettling refugees from Syria in the United Kingdom. She was one just a few supporters of Liz Kendall in last summer’s Labour leadership contest, but she was also one of the MPs willing to put Jeremy Corbyn’s name on the ballot. If anyone personified the kind of rising star who could carry forward the center-left policy perspective of ‘Blairism without Blair,’ it might reasonably have been someone like Jo Cox.

She was also a passionate product of Yorkshire, and she was genuinely proud of the fact that she grew up in Bentley and that she never lost touch with her roots in that community, indeed the community where a deranged killer ended what should have been decades more of public service.

If you’re on the right, you can do no worse than Alex Massie’s tribute today in The Spectator. If you’re on the left, you can do no worse than Polly Toynbee’s column in The Guardian. Both make much of the tone that’s characterized the referendum campaign.

It’s too early to know why the gunman did what he did and, in some cases, it’s perhaps impossible to know, ever, what drives a human being to kill another one. Whatever the motive, it will — and should — force a much more tranquil and reasoned tone to the referendum debate, a necessary tonic after weeks of frenzied and often harsh exchanges on the economy, Britain’s role in the world and immigration.

Chancellor George Osborne, who is one of the Conservative Party leaders on the ‘Remain’ side, all but tried to blackmail British voters earlier this week when he argued that he would have to introduce a more restrictive 2015 budget with tax increases and spending cuts in the event that British voters opted to leave the European Union. Just this morning, Nigel Farage, the leader of the United Kingdom Independence Party unveiled a giant poster that screams ‘BREAKING POINT’ with a photo of Syrian refugees from last summer — the clear message from the Leave campaign is that, outside of the European Union, a British government will be able to keep out those nasty immigrants.

If there’s any silver lining here (and there’s not), it might be that the week that follows will see a more subdued, more responsible and more sober-minded debate over the benefits and drawbacks that would befall the United Kingdom if it left, after 43 years, the European Union — a membership that it spent nearly a decade trying to win in the 1960s and 1970s in the face of French resistance. It is a momentous decision, and it’s a disservice that so much of the campaign’s debate is steeped in fevered emotions and not dispassionate facts.

Americans will note that today’s tragedy felt uncannily like the attempted murder six years ago of Gabrielle Giffords, the former Arizona congresswoman who survived gunshots to her head from a similarly violent and deranged gunman. After years of therapy, has recovered much of her ability to function. Of course, Cox didn’t make it; Giffords did, and it was heartbreaking to read Giffords’s statement today that Cox’s murder ‘sickened her.’ It’s even more numbing after an attack early Sunday morning at Pulse, an Orlando gay club, that killed 49 people in the most deadly mass shooting in recent American history.

But as an American, I also remember the sadness that fell on Minnesota’s 2002 Senate race, when a beloved incumbent, Democrat Paul Wellstone, was killed in an airplane crash. Former vice president Walter Mondale stepped up to the challenge to run in his place, but the memorial service for Wellstone took on such a politicized tone that appalled voters instead elected the Republican candidate, Norm Coleman. There’s a lesson here, and both the Leave and Remain sides should take heed. Even in the midst of such a hard-fought campaign, there is nothing to be gained from politicizing a tragedy and everything in presenting a unified face of dignified  restraint.

 It’s absurd to argue that, given the political climate and debate in Britain today, the referendum campaigns didn’t play a role in the background to Cox’s assassination. At first glance (and only at first glance), it appears there was a political motivation to the murder. But we don’t know the facts, we know little about the killer or his background, including his mental state. But neither Osborne nor Farage nor prime minister David Cameron nor ‘Leave’ proponent and former London mayor Boris Johnson nor ‘Leave’ proponent and current justice minister Michael Gove killed Cox.

We’ll probably never know what would have happened in next Thursday’s vote in the lack of today’s tragedy. It’s possible that one side will gain votes as a result. Historians for decades will attempt to ask, ‘What if?’ Next Thursday’s vote will always be horribly interlinked to today’s craven murder. But it’s now more important than ever that the leaders of the two campaigns rise above today’s tragedy to guide British voters to a dignified end to a referendum campaign that’s now sullied one of the world’s most enduring democracies with a disgraceful scar of political violence.