This Saturday, on January 21, I'll be marking Donald Trump's first day in office by marching in Sydney to stand up against the hatred and bigotry he represents.

The Women's March on Washington was organised — predominantly on Facebook — for the day after inauguration day to protest against Mr Trump's politics and the threat he poses to the safety and autonomy of the politically vulnerable: women, religious minorities, racial minorities, LGBTI communities and people with disabilities.

"The Women's March on Washington will send a bold message to our new government on their first day in office, and to the world, that women's rights are human rights," the organisers say on their website.

"We stand together, recognising that defending the most marginalised among us is defending all of us."

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It's expected that more than 200,000 people will walk from the Lincoln Memorial to the White House the morning after Mr Trump's inauguration.

Meanwhile, some estimates suggest an unusually low number of people will be attending Mr Trump's inaugural ceremonies; there are currently more bus parking applications for the women's march than there are for the inauguration itself.

Sister marches inspired by the Women's March on Washington have also been organised in cities the world over, including in Australia.

In Sydney, the Women's March is teaming up with groups like Grandmothers against Detention of Refugee Children NSW to create an inclusive protest that targets all transgressions of human rights and dignity.

Of course, Mr Trump's domestic policies won't directly affect Australians, but organisers of the Sydney march argue it is about more than that. It's about standing with vulnerable groups across the globe to fight bigotry and division.

But perhaps more importantly, it's about reminding Australians that some of the ideas we find so offensive in Mr Trump have taken hold in our own politics, too.

'If something needs fixing … do some organising'

In his final address as president last week, Barack Obama implored Americans to "show up" and help do the work that needs doing".

"If something needs fixing, lace up your shoes and do some organising," he said.

Michelle Obama issued a similar call to arms back in October, when the world first heard the horrifying tape in which Mr Trump described and condoned sexually assaulting women.

She said we need to do what we as women have always done: Roll up our sleeves, and get to work.

Which is exactly why I'm marching.

I'm marching because electing Mr "grab her by the pussy" sends a message to sexual assault victims that we still aren't listening, and confirms the suspicion of so many women that they are never truly safe.

It's a reminder for potential perpetrators of sexual assault that they have no reason to fear concepts like accountability, punishment, and justice.

Donald Trump's "locker room talk" prompted many women to protest as part of the #PussyGrabsBack movement. ( Reuters: Eduardo Munoz )

I'm marching because electing a man who wants to punish women who seek abortions restricts every woman's autonomy.

Electing a government that seeks to defund women's health services and strip them of their reproductive rights is an insult to the dignity of women everywhere.

And we know now that this is not just campaign bluster.

Mr Trump has released a shortlist of five predominantly pro-life judges from whom he will nominate the next Supreme Court Justice, one of whom believes the landmark Roe v Wade decision that opened the gate to abortion access for American women is "the worst abomination of constitutional law" in American history.

The US is not so different to Australia

I'm marching because electing a president who supports transphobic laws sends the message to the LGBTI community that there is no hope of progress.

Last July Mr Trump spoke out in support of a North Carolina law barring transgender people from using bathrooms that best match their gender identity, as well as banning local governments from passing LGBT anti-discrimination law.

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I'm marching because electing a man who forged a presidency from the idea of building a wall to solve immigration issues serves to legitimise our own Government's Pacific island processing camps.

Indeed, America is not as different to Australia as we like to tell ourselves; our Government does not shy away from stripping asylum seekers, Indigenous Australians, women, and LGBTI communities of their rights, either.

Of course, there are many who believe the march is pointless — that it has no clearly articulated aims and will have no tangible outcomes.

For example, some anti-Trump women have said they think the march could potentially further divide Americans, while others believe the effort that goes into attending a march that could "be easily dismissed with a presidential tweet storm" might be better invested elsewhere.

But in a democracy, expressions of large-scale public opposition matter because they remind politicians that the groups they demean in order to win elections don't disappear, and they can make the business of governing very difficult if they try.

Moments that galvanise people matter, even if it's not immediately clear how

When it became clear that Mr Trump would win the election, one of my closest friends sent me a message that said: "I promise to always do my best to keep you safe."

She knew that for all the complex political analysis that would follow, when you, as a woman, realise that a man who publicly condones and has possibly committed sexual assault becomes president, in that moment the only things many women felt were isolation and fear.

That's why protests matter. Marching alongside hundreds of allies and receiving messages of love and support from friends serve the same purpose: they empower people in remarkably disempowering situations.

So yes, I'm marching against Mr Trump. But mostly I'm marching to support the women he has belittled and all the groups his bigoted populism will threaten.

And I'm also marching for me.

If 2016 has taught me one thing, it is that no progress is permanent. And if we don't get organised, and get to work, we could stand to lose it all.