"This doesn't end today," Evan Greer, campaign director at advocacy group Fight for the Future, which helped lead the demonstration, said in a statement. "This protest is the kickoff of a sustained campaign to keep the pressure on lawmakers and the FCC to do the right thing. This is just our opening salvo, and it's a massive one."

Open internet activists hailed Wednesday's massive online demonstration of support for net neutrality as a major success, but warned that the fight to stop the Trump administration's plan to dismantle US net neutrality rules is only just beginning.

The FCC's current net neutrality policy, which prohibits broadband giants like AT&T and Verizon from favoring some online services over others, is vital to ensuring that the internet remains an open and dynamic platform for economic growth, digital innovation, and free speech, activists say. Americans from across the political spectrum agree, recent polling suggests .

Moreover, because of the way the FCC is structured, Pai, as chairman, effectively controls the agency's agenda and can ram through his priorities on a partisan basis. A FCC spokesperson declined to comment on Wednesday's protest or Pai's response to it.

Pai, a former Verizon lawyer and longtime FCC official who was chosen by Trump to lead the agency in January, has made dismantling the Obama-era net neutrality protections a top priority. Last year he famously pledged to take a "weed whacker" to the net neutrality policy , and there is no indication that he is having second thoughts. Pai has a reputation as a conservative ideologue—his speech announcing the net neutrality rollback was sponsored by the right-wing activist group FreedomWorks —and it would be a startling turnabout if he bowed to public pressure and scrapped his plan.

There's no sugarcoating the reality: Net neutrality advocates know they face an uphill battle. That's because their primary adversary, Republican Federal Communications Commission chief Ajit Pai, who is not an elected official and is therefore not directly accountable to voters, appears to be hell-bent on rolling back the agency's open internet rules.

"Net neutrality ensures that the free market—not big cable—picks the winners and losers," Reddit co-founder Alexis Ohanian wrote in a blog post on Wednesday. "This is a bipartisan issue, and we at Reddit will continue to fight for it. We've been here before, and this time we're facing even worse odds."

"But as we all know," Ohanian added, "you should never tell redditors the odds."

By any measure, Wednesday's "Day of Action" was an impressive display of online political organizing. By late Wednesday, protest leaders reported that more than 125,000 websites, organizations, and internet users took an active part in the demonstration, and more than 10 million people saw pro-net neutrality messages on participating websites. The demonstration included some of the internet's most popular websites and services, from Netflix to Pornhub, both of which offered simulated "throttling" of their streaming video to show what could happen in a post-net neutrality world.

"We're going to stick with this fight for as long as it takes to preserve the open internet protections the majority of Americans demand."

Organizers said they had collected more than 1.6 million net neutrality comments to the FCC, apparently breaking the previous single-day record from the 2014 "Internet Slowdown," as well as nearly 3.5 million emails to members of Congress, which will be delivered in the coming days.

If Pai is successful in his anti-net neutrality crusade, he will have delivered a major gift to the nation's largest telecom firms, which hate the FCC's policy because it subjects them to a strict regulatory regime known as Title II, which was originally designed for the traditional phone system. Pai won't pay an immediate price at the ballot box for his efforts, but he is accountable to Congress, which has oversight of the FCC. That's why some net neutrality activists are increasingly turning their focus to Capitol Hill.

"Lawmakers in Washington, DC need to understand that if they stand idly by and allow the FCC to gut these rules that are overwhelmingly supported by voters from across the political spectrum, they will be seen as enemies of the internet and enemies of free speech," said Greer.

Here, too, activists face a steep challenge, because Congress is controlled by Republicans, many of whom have long railed against the FCC's net neutrality policy, including Rep. Marsha Blackburn, the Tennessee Republican who chairs the influential House Energy and Commerce Subcommittee on Communications and Technology, which has oversight of the FCC. Blackburn has received hundreds of thousands of dollars in campaign donations from telecom interests.

Despite the steep odds, net neutrality advocates vowed to build on the momentum from Wednesday's protest. Candace Clement, campaign director at DC-based advocacy group Free Press Action Fund, which helped organize the protest, pledged in a statement to "stick with this fight for as long as it takes to preserve the open internet protections the majority of Americans demand."