BOSTON (Reuters) - The protests in major U.S. cities against Republican Donald Trump’s surprise presidential election victory have been impromptu affairs, quickly organized by young Americans with a diverse array of backgrounds and agendas.

NYPD officers keep an eye on people taking part in a protest against Republican president-elect Donald Trump at the Washington Square park in the neighborhood of Manhattan in New York, U.S., November 11, 2016. REUTERS/Eduardo Munoz

But as they look out at the next four years with Trump in the White House while his party controls both houses of Congress, activists are starting to prepare for what they hope will be the nation’s strongest protests since the Occupy Wall Street movement.

Rallies scheduled for Saturday in New York and Los Angeles, and a protest planned for Washington on Jan. 20, when the New York businessman succeeds President Barack Obama, will be just the beginning, activists said in a series of interviews.

The Rev. Al Sharpton, a civil rights leader from New York, said anti-Trump protesters should borrow a page from the playbook that Republicans used to oppose Obama’s policies.

That movement started organically, later developed as the Tea Party movement and eventually resulted in the election of Trump, said Sharpton, whose National Action Network plans to launch a new organizing effort at its New York headquarters on Saturday.

“We are not going to be as ugly as them, but we are going to be just as persistent,” Sharpton said. “This is not going away.”

Sizable protests sprung up this week in about a dozen major U.S. cities, including Boston, Baltimore and San Francisco. Demonstrations in Portland, Oregon, and Berkeley, California, turned violent, with protesters setting fires and clashing with police.

Trump initially dismissed the crowds on Twitter, calling them “professional protesters, incited by the media,” but later reversed course, saying he admired their “passion.”

PLANS TO BE ‘FORCEFUL’

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T.J. Wells, who had volunteered to work for Democrat Hillary Clinton’s failed presidential campaign, said his decision to organize a Thursday night protest at Washington’s Trump International Hotel near the White House was spontaneous.

“I literally shared it with a few friends, and within a few hours I had a couple hundred people show up,” said Wells, who is 27 and lives in the Washington suburb of Bethesda, Maryland, where he works in human resources.

He said he hoped it would be the first of many such demonstrations.

“From Inauguration Day to the time he’s out of office, we have to make sure that if there’s something he’s going to pass that the majority of Americans who voted for Hillary Clinton are not OK with, that we are forceful about that,” Wells said.

Some 59.5 million people voted for Trump, fewer than the 59.7 million who cast ballots for Clinton, but Trump’s strong showing in swing states, including Michigan, earned him a decisive victory in the Electoral College that ultimately picks the president.

Opponents have cited Trump’s history as a leader of the “birther” movement that claimed wrongly that Obama had not been born in the United States, his promises to deport the estimated 11 million undocumented immigrants in the country and his calls to register Muslims.

Members of the ANSWER Coalition, a broad-based U.S. protest group, have marched in this week’s protests and aim to draw tens of thousands to an anti-Trump Inauguration Day rally, said Walter Smolarek, an organizer.

“The people are going to fight back against the Trump agenda from day one,” Smolarek said. He said the group planned to continue to protest throughout Trump’s four-year term.

Since his victory on Tuesday, Trump has taken a more measured public tone than he had during the campaign. That has some civil-rights advocates ready to wait and see what Trump does before joining in protests.

“I don’t think that Donald Trump responds very well to protests, to be honest with you,” said Brent Wilkes, national executive director of the League of United Latin American Citizens.

He said he was willing to see whether Trump would be more moderate in his actions than he had been in the campaign, adding: “If he doesn’t, we’ll be out there in the streets.”