“Kyrsten Sinema sold us all out.”

“Kyrsten Sinema facilitates fascism!”

“Parents: make sure to give your children all the attention they need, so they don’t grow up to be Kyrsten Sinema.”

Social media posts like this targeting Senator Kyrsten Sinema accrued hundreds of thousands of likes and shares this week.

What did the maverick Arizona Democrat do to prompt this unhinged outrage? Simply take a stand for the filibuster, part of our system of checks and balances that keeps us free, a position that until quite recently was uncontroversial even among Democrats.

“The danger of eliminating the 60-vote threshold is that the Senate becomes the House,” Sinema said at an event earlier in the week. “And I remind everyone, I left the House and ran for the Senate for a reason.”

The senator made a compelling case for maintaining the Senate filibuster, which requires 60-votes to pass legislation instead of a bare majority, 50 votes.

“When Republicans are in control, they pass a little bit of crazy legislation,” she argued. “When Democrats are in control, they pass a little bit of crazy legislation. And the job of the Senate is to cool that passion.”

In sharp contrast: The Humiliation of Joe Manchin.