Twitter’s initial announcement, made in a series of tweets by Jack Dorsey, its chief executive, stunned the tech and political communities. Even though political ad spending on Twitter is minuscule compared with the amount on Facebook — the 2020 presidential campaigns have spent $60 million on Facebook this year , according to the tracking firm Advertising Analytics, but just $4 million on Twitter — the idea of banning all political advertising on the platform was still a surprise.

And it set Twitter apart from Facebook and Google, which have not suggested they would take any similarly drastic actions. Mark Zuckerberg, Facebook’s chief executive, has said he will allow even false political advertising on his platform because it is newsworthy.

When Twitter finally rolled out the details of its new policy on Friday, it turned out not to be a blanket ban on all political advertising; some exceptions for issue ads were included. Essentially, all candidates, parties, super PACs and political groups would be turned away. Issue advocacy would be permitted so long as it didn’t expressly endorse specific candidates, ballot measures, legislation or judicial decisions, but these advertisers wouldn’t be able to microtarget specific audiences.

In the Democratic field, candidates largely praised the decision, lest they be seen as supporting the platforms’ hands-off policies of the past that have allowed foreign states and other groups to sow disinformation. But at least three campaigns had spent roughly $1 million each on the platform — Senators Kamala Harris and Elizabeth Warren, and former Representative Beto O’Rourke, who recently dropped out — in part to try to capitalize on major news events.