My wife Jo Cox was murdered in her constituency in 2016. The alleged attack on Helen Haines is a punch to the gut | Brendan Cox

It’s never a good sign when you turn on your phone to find a dozen messages asking if you are OK. For reasons you will come to understand, I only get those messages when something awful has happened.

So yesterday, when I came out of an all-day meeting on antisemitism and picked up the messages from friends, I clicked across to check the news with real dread. The last time I’d received a similar barrage of messages was when former UK MP Ann Widdecombe was killed earlier this year.

As I read the news about the alleged attack on Australian MP Helen Haines, the dread I felt was followed by what I can best describe as a punch to the gut. A wave of shock. Deep sorrow. The despair that another elected representative had been so brutally injured.

Jo Cox MP, my late wife, was murdered in 2016 in her constituency in Yorkshire, England by a far-right extremist as she went about her constituency work.

Helen’s story reminded me of what happened to Jo. Both incidents took place in a small town far from the corridors of power. Helen, like Jo, clearly has a deep connection with her community. Even their names connected them (Jo’s first name was Helen – though she always used Jo as her main name).

When something like this happens it’s impossible not to feel yourself back in the moment of your own loss. My immediate reaction yesterday was to hope to God she survives – I remembered how I prayed the same as I heard the news about Jo’s attack.

I quickly worried about her family, the impact on them, and immediately recalled the impact on mine.

And then of course you worry about the impact on the country, its democracy and the values that underpin it.

Practically – unless you are part of her medical team – there is not much that most Australians can do to help Helen directly. Or even to comfort her family (though public solidarity really does matter). But what you can do is be part of the response.

I don’t know what motivated the alleged attack on Helen, which is still under investigation. And I’m not sure I care. Whatever the motivation, it damages democracy. And there can only be one appropriate response: to work together to strengthen it.

I know from bitter experience that moments like these can become turning points. They can reinforce our divisions, fuel our anger and make us more fearful of one another. Or they can remind us of what we stand to lose when hatred and intimidation are allowed to shape our public life and brutalise our democracy.

After Jo was killed, I saw extraordinary acts of kindness and solidarity. People who had never met her came together to celebrate her life and the values she represented. They reached across political, religious and cultural divides. They refused to let an act of hatred have the final word.

That response mattered then, and it still does today.

Across democracies, political debate is becoming more hostile. Opponents are increasingly portrayed not merely as people who are wrong, but as enemies who must be defeated at any cost. Online, contempt is rewarded, threats are normalised and people are encouraged to see the worst in one another.

We should be alarmed by that. But alarm alone is not enough.

We cannot undo what happened to Jo. We cannot take away the pain of those affected by the alleged attack in Australia. But we can decide what kind of society we build in response.

We can allow violence to make us more divided, more suspicious and more fearful. Or we can use this moment to reaffirm our commitment to democracy, decency and what we have in common.

The measure of a society is not what shocks it experiences, but how it responds. Australians cannot undo what is done, but you can still shape what it means.

• Brendan Cox is the co-founder of the Together Coalition, which acts as the secretariat for the Independent Commission on Community and Cohesion. He’s also co-founder of the Jo Cox Foundation, Survivors Against Terror and More in Common