Donald Trump has provoked plenty of protest in his day, a period that, alas, will continue for at least a while. I’ve been trying to figure out which causes and constituencies are likely to be able to generate sustained, diversified, and potentially influential campaigns while he’s president.

Despite his repeated claims to the contrary, Trump is provocative, offensive, and unpleasant–at least in public. But Trump’s persona, reliable as it is, isn’t enough of a base for a winning political campaign. The Clinton campaign proved this. Sustained and effective activism is going to be based on policies and constituencies.

People who study social movements argue about what causes develop when, and the Trump era provides a new test.

One school of thought suggests that effective protest movements are likely to flourish when they enjoy support from allies in government. The iconic era of the civil rights movement took place in the wake of Brown v. Board of Education, punctuated by dramatic and effective campaigns in the early 1960s, when a president rhetorically supported claims for civil rights.

Another approach emphasizes the movements that grow in opposition. Just a little later in the 1960s, the movement against the Vietnam war grew larger and more volatile, focused squarely on the president who was prosecuting that war. Environmental, peace, gay, and reproductive rights activists have effectively targeted unwanted policies from conservative politicians to turn out their crowds, generating support and contributions. Already, the unwelcome election of Donald Trump has generated a windfall of financial support for Planned Parenthood and the American Civil Liberties Union.

My hunch is that groups that are generally marginalized need visible institutional allies to get the room to mobilize, while those that can normally function in institutional politics take to the streets when they get shut out.

If this is right:

The Trump era should see strong campaigns from a broad range of already organized groups, like those supporting reproductive rights, environmental action, and immigrants’ rights and welfare. They, and others, will rise to contest the policy changes Trump pushes. The enormous mobilization of Women’s marches across the United States, featuring a broad coalition of diverse groups deeply troubled by the likely policies of the Trump administration, supports that view.

But, it’s unlikely to be just organizations and activists on the political left. The racist right, explicitly marginalized by mainstream Republicans for a generation, found space and some tolerance in the Trump campaign. Under the rubric of the “alt.right,” neo-Nazis, the Ku Klux Klan, and others have organized more openly than I can ever recall. They view the Trump presidency with eager anticipation of spreading the word. Richard Spencer, white nationalist leader, explained: “Is Trump the answer? No. Is Trump the first step, hopefully, toward identity politics? Yes. That’s what got me so excited about him.”

Large and powerful movements emerge when people believe that protesting is both necessary and potentially effective. I suspect there’s more than enough urgency and uncertainty for many movements.

And, of course, the stakes involve more than an academic debate.