Rep. Marsha Blackburn (R-Tenn.) at the Republican National Convention in July. (Eric Hanson for The Washington Post)

Rep. Marsha Blackburn launched her Senate election bid — as so many people do — with a video explaining what she believes in. But she can't use it as a campaign ad on Twitter.

Twitter told the campaign Monday that it couldn't pay to promote the video — in which the Tennessee Republican claims that she stopped “the sale of baby body parts,” a reference to her opposition to fetal-tissue research — as an advertisement. Twitter told the Blackburn campaign that the ad was “deemed an inflammatory statement that is likely to evoke a strong negative reaction,” campaign spokeswoman Andrea Bozek told The Washington Post. This is the same justification the company has used to block antiabortion ads before.

Blocking the video from being posted as an advertisement limits its reach. But it doesn't stop anyone from viewing it. Blackburn's video is still up and running after she tweeted it out on her own account. So, while it may be objectionable as fodder for advertisement, it's clearly not seen as objectionable enough to take down from Twitter altogether. It can be shared by retweet, and since Blackburn's campaign went public with the ad rejection, the video has been retweeted at least 18,000 times.

Which gets to the crux of the matter: Twitter and other social media platforms have made plenty of rules about what is and isn't acceptable on their sites. But those rules govern a messy swamp of expression and, even to an informed observer, are about as clear as mud.

The Blackburn campaign saw Twitter's decision as politically motivated censorship. In a campaign email, Blackburn said the block on her advertisement illustrated how “Silicon Valley elites” are imposing their values on the general public. “Silicon Valley is in the pocket of the liberal establishment, but our conservative revolution is going to keep on winning,” Blackburn said.

Twitter said in a statement that it has different guidelines for what is acceptable in its promoted ads and what it deems appropriate for more general tweets. That's because advertising gives accounts a much broader reach. If someone wants to seek out Blackburn's opinions, they can follow her Twitter account or navigate to her feed. An ad, however, reaches people who have not actively sought out Blackburn's opinions in those ways, and therefore the company holds it to a different standard.

But even clear lines — i.e., different sets of policies for advertisements and all other content — get blurry when looking at free expression in the digital age. And that's how we end up with a video that's deemed acceptable for sharing but not for advertising.

Meanwhile, Twitter and other platforms continually find themselves in uncomfortable situations that make them look inconsistent — even when they're abiding by their own rules — and result in them ruffling feathers across the board.

It may make sense to Twitter, Facebook and others to be more stern about their ad policies, considering the scrutiny that they are facing over questions on Russian-funded advertisements, experts said. Twitter is known for being historically lenient on speech, making this feel like a major crackdown, said Kate Klonick, resident fellow at the Information Society Project at Yale Law School.

But she said Twitter has been inconsistent in its approach, leading to further issues. “It feels like a lot of these decisions are not being made with consideration about where they will lead [Twitter] down the road,” she said. The social media network, for example, recently said that President Trump could say things other Twitter users would not be allowed to say, because he is a newsworthy public figure. But, Klonick said, couldn't that description also fit Blackburn, a congresswoman and Senate candidate? “It's an insanely slippery slope to draw lines between people,” she said.

In this case, the Blackburn campaign has used the incident to burnish its conservative credentials. Blackburn demanded an apology from Twitter on Tuesday. The campaign also created a GIF that shows the Blackburn campaign's Twitter timeline with the word "BANNED” stamped on it.

You can see it — where else? — on the campaign's Twitter account.