On Wednesday evening I was at the Baileys book prize bash. Now in its 20th year, the best novel of the year – by a female novelist writing in English – was won by debut Irish novelist Lisa McInerney. This is always a sparkling, joyful evening when it feels good to be a woman and optimism flies high. This year many invitees were further buoyed up by the news that Hillary Clinton had won the presidential nomination for the Democratic Party.

For an American feminist at the post-award party, this was most portentous and pivotal win ever in the electoral history of the US: 'This is as important as the Civil Rights Movement. She is our Martin Luther King. No women has ever got this far. Male power is going down and out. Our time has come. This changes everything.' I too was carried away by the high emotion, by feminist ecstasy. How could I not be? Hillary has undeniably made history.

She made a rousing speech to her supporters: 'This victory belongs to the generations of women and men who struggled and sacrificed and made this moment possible'. The struggle has indeed been long. In 1872 Victoria Woodhall, member of the Equal Rights Party put her name forward as a presidential candidate. In 1916, Jeanette Rankin became the first female elected to Congress. These gutsy women came forward before there was universal female suffrage in their country. From then to now, more women have entered Congress and the Senate but never come close to the top job.

But I do not think that this will 'change everything'. Clinton described it as a moment and that's what it is, a seismic moment. Those who fizz with hyperboles will, for sure, have their over-high expectations dashed. Hillary is already being attacked by socialist American women who see her as a 'warmongering neo-liberal' and friend of the rich, both valid accusations. She may be a progressive Democrat when it comes to domestic policies, but her foreign policies have been and are infused with superpower arrogance.

Hillary Clinton
Democratic presidential candidate former Secretary of State Hillary Clinton greets supporters during a primary night event on June 7 in Brooklyn, New York.Getty Images

I do hope she beats Trump, that she shows the disgusting sexists who have stalked and demeaned her for so many years. However, I am braced for the inevitable turnabouts and betrayals, scepticism and anger too when she acts exactly like every US president has done, perhaps must do. Hillary's femaleness will not ameliorate policies or practices. Power warps principles.

Promises and possibilities seem to vaporize after they get into office. A new realism sets in.

This is what happened with Obama. Anti-racists from north to south, east to west, danced in the streets, thought the world had finally been wrested from the white elites of the west. I wore a T-shirt with his picture on my chest.

Much of those wild hopes came tumbling down over the years. The first black president of the USA promised to shut down Guantanamo Bay. He didn't. Extra-judicial killings and drone attacks – which he and Clinton authorised – killed civilians in Pakistan and Afghanistan and made his sonorous oratory sound hollow. Police killings of black people go on and are unpunished. Of those shot dead by law enforcers, 29% were black men and women. Poverty and injustice persist. It is unfair to blame him for all these ills. It's what happens.

Sadiq Khan
Sadiq KhanGetty Images

This will happen to Sadiq Khan too, our new mayor of London. The son of a British Pakistani bus driver, who was demonised by right-wingers, beat the wealthy, entitled Zac Goldsmith. Millions of us were understandably rapturous. As were thousands of voters in Bristol where a young, mixed race man, Marvin Rees, brought up by a lone mother on council estates, beat George Ferguson, the white, well off and popular ex-Mayor.

Within a few weeks, Rees has confessed he will have to make 'tough choices' and cuts. Khan will undoubtedly dishearten his left wing and minority supporters because as London's mayor he cannot be beholden to any one interest group or political faction. These incumbents who broke through barriers soon learn that established systems and structures hold out against fundamental change or reform. Promises and possibilities seem to vaporise after they get into office. A new realism sets in.

All that said, these democratic insurrections and upheavals really do matter. Young females will be inspired by Hillary to think big and go for it. Khan and Rees will encourage working class men and women, Muslims and others to aspire and imagine the impossible. In the distant future, key institutions will no longer be controlled by mono-racial, privileged cliques. Diversity will not have to argue or beg for entry. It will be valued highly. Set old ways will become redundant.

I won't be around to see those political and social transformations, but the day will come. And it will come sooner because Obama, Clinton, Khan, Rees and others, dared and won.