WASHINGTON, United States (AFP) — Hundreds of thousands of protesters spearheaded by women’s rights groups are set to converge on Washington Saturday to send a defiant message to America’s new president, Donald Trump.

The flag-waving crowds who turned out to cheer Trump’s inauguration will make way for a coalition of protesters who fear an erosion of women’s rights under the new Republican administration.

Powered by social media, the “Women’s March on Washington” aims to draw 200,000 people, illustrating the divisions of a country whose incoming leader faces levels of public mistrust unseen in recent decades.

Trump’s inaugural speech on Friday set the tone for his presidency: proudly populist, fiercely nationalist and determined to break with the legacy of his Democratic predecessor.

His first act in office — signing an executive order aimed at freezing Barack Obama’s signature health care law, before it is eventually repealed — was a potent gesture in that direction, with more such actions expected to follow on Monday.

Trump’s official schedule for Saturday, his first full day in the world’s most powerful job — includes just one engagement, a multi-faith service at Washington National Cathedral at 9:30 am (1430 GMT).

But less than 24 hours after entering the White House, Trump will be faced with a show of force by demonstrators united by a common dread of what his presidency holds in store.

Backed by celebrity participants including Scarlett Johansson and Michael Moore, Saturday’s march comes on the heels of a first day of anti-Trump protests marred by sporadic outbreaks of vandalism, with windows smashed downtown and more than 200 people arrested.

Authorities will be on alert for any new flare-up of violence — although the stated goals of the women marchers are resolutely peaceful.

One participant, 37-year-old Jessica Vroman from Sacramento, California, posted a picture of women packing a flight bound for Washington.

“It is FULL of women — all ages, all races — going to the march. We are singing, high-fiving and taking selfies. This what hope looks like people!” she wrote.

Trump’s campaign was marred by sex assault allegations, fat-shaming a former beauty queen and a controversial stance on abortion.

While Trump nonetheless won 42 percent of the women’s vote, millions who did not vote for him worry that gender rights and other progress on women’s health, contraception and abortion could be chipped away.

“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,” organizers said in a statement.

They have not specifically used the term “anti-Trump” to describe their efforts, but the message is clear.

Bringing together “people of all genders, ages, races, cultures, political affiliations and backgrounds,” organizers say the protest march seeks to secure immigrant rights and access to abortion services, among other demands — things which Trump’s critics accuse him of wanting to curb.

Dozens of progressive organizations are supporting the event, as well as Amnesty International and Planned Parenthood, the women’s health care provider that is a Republican target because of the abortion services it provides.

The marchers secured the right to gather from 10:00 am (1500 GMT) on the National Mall — the site where Trump was sworn in as America’s 45th president, and which his supporters failed to fill to capacity on Friday.

The Women’s March began with a simple Facebook post from Hawaii grandmother and retired lawyer Teresa Shook to about 40 of her friends. 

Word traveled quickly, and eventually made it to the pro-Hillary Clinton Facebook group Pantsuit Nation, which has nearly four million members.

Nearly 225,000 people have said on Facebook they will attend. Another 250,000 said they were interested.

Women across America have knitted more than 60,000 pink “pussyhats” — with cat ears — for the marchers to wear, in a bid to claim back the derogatory term used by Trump in a hot-mic boast about groping women’s genitals.

Though a mass turnout is no guarantee, at least 1,200 buses have asked for parking permits at Washington’s RFK Stadium for the protest day — far more than for the inauguration itself.

Some 300 sister marches are being held across the country, from New York to Boston, Los Angeles and Seattle, as well as cities around the world.