In the hours and days after a mob of President Trump’s loyalists stormed the Capitol, the nation’s biggest tech companies began to shut down accounts that helped incite the rampage. In the days and weeks before the attack, President Trump had used his Twitter feed and Facebook page to spread the lie that he had won the November election. It was that falsehood that helped drive the mob to the Capitol last Wednesday after a speech by the president.

Facebook said the risks were too great to allow the president’s posts. Twitter followed suit. The focus shifted to Parler, a favorite app for right-wing figures. Citing posts on Parler that encouraged violence and crime, Apple and Google removed the app from their app stores. Then Amazon stopped hosting it.

For Big Tech, the events of the past week raised tricky questions about politics, free speech and radicalization of people online.

How Parler, a Chosen App of Trump Fans, Became a Test of Free Speech

The app renewed a debate about who holds power over online speech after the tech giants yanked their support for it and left it fighting for survival. Parler went dark on Monday after Amazon’s web hosting platform shut down Parler’s account.

Stripped of Twitter, Trump Faces a New Challenge: How to Command Attention

The president became a celebrity through television, but Twitter had given him a singular outlet for expressing himself as he is, unfiltered by the norms of the office.

Amazon, Apple and Google Cut Off Parler, an App That Drew Trump Supporters

The companies pulled support for the “free speech” social network, cutting the service off from its users just as many conservatives are seeking alternatives to Facebook and Twitter.

Twitter Permanently Bans Trump, Capping Online Revolt

The president’s preferred megaphone cited “the risk of further incitement of violence.” It acted after Facebook, Snapchat, Twitch and other platforms had placed limits on him.

Facebook Bars Trump Through End of His Term

Mark Zuckerberg, Facebook’s chief executive, said the risks of Mr. Trump using the service were too great.

In Pulling Trump’s Megaphone, Twitter Shows Where Power Now Lies

The ability of a handful of people to control our public discourse has never been more obvious, writes our columnist Kevin Roose.