When large demonstrations work, they change the conversations afterward. Assembling in Washington DC–and elsewhere–occupies space in mainstream and social media even when the demonstrators have gone home.

Last week’s tax march, which turned out tens of thousands across scores of American cities, focused squarely on the release of Donald Trump’s tax returns.

It made for clever politics in a few different ways:

First, Tax Day protests are a staple for conservative activists, who accentuate widespread resentment toward filling out complicated forms and spending money on anything you might not feel like spending money on that day. The Tea Party emerged as a force through Tax Day protests in 2009, and “Tea” stood for: Taxed Enough Already.

Until last week, Tax Day protests read as resentment toward paying taxes and supporting government altogether. By claiming this space, Tax Day activists flipped the script to focus on tax justice instead. Donald Trump’s hidden returns allowed activists to talk about tax advantages for the very rich, and to establish a strong position against tax cuts for corporations and the very rich that float high on the Republican agenda.

Second, Trump’s supporters have claimed, as he has, that the November election demonstrated no public interest in the president’s returns. Large numbers of marchers demonstrated otherwise. Although they didn’t provide the returns, Trump’s allies and staff were once again forced to provide (unsatisfying) answers.

Third, continued attention to the secret returns will haunt any Congressional debate about tax reform. Democratic legislators promised not to support any changes to the tax code until they can see how they will affect Trump’s finances. They demand that he demonstrate that he’s looking out for the country rather than himself.

Fourth, because the president is so sensitive to criticism–and so difficult for his staff to manage–every provocation trolls, providing Trump the opportunity to tweet another unforced error. He rarely misses such opportunities: on Twitter, he wondered aloud who had paid for the demonstrations. Activists could easily respond that they’re just interested in who paid for Trump.

Today’s March for Science in Washington, DC, supported by hundreds of satellite marches worldwide will work, partly, by drawing attention to public support for science and education and to the role of facts and inquiry in making public policy.

Activists are directly challenging the notion that the president’s substantial gut should serve as the ultimately arbiter on climate change, public health, or transportation. The science marchers support a passionate commitment to a process for coming to truth, one which should inform the public debate.

I’m inspired.

Apparently, Trump is as well. In response to the march, the White House released a statement affirming the president’s commitments to science and economic growth–but not addressing climate change:

My administration is committed to advancing scientific research that leads to a better understanding of our environment and of environmental risks...As we do so, we should remember that rigorous science depends not on ideology, but on a spirit of honest inquiry and robust debate.

The maxim that “hypocrisy is the tribute vice pays to virtue” (from Francois de La Rochefoucauld, a 17th century French writer), suggests that such rank duplicity actually ends up reinforcing nobler norms.

I expect fine journalists to report on the march and Trump’s response to it. I also expect them to outline Trump’s proposed budget, which features massive cuts to science generally, medical research, and environmental protection.

The effective demonstration provides a torch to enlighten–or inflame–the discussions that follow.