Over the past few weeks, as Senate Democrats really started pushing voting rights, Sen. Kyrsten Sinema (D-Ariz.) has quietly become their primary obstacle. And now, unfortunately for Democratic leaders, she’s expressing her opposition loudly.

“I will not support separate actions that worsen the underlying disease of division infecting our country,” she said in a speech Thursday in the Senate defending keeping the filibuster intact — ensuring that voting-rights legislation will be blocked by Republicans.

Sinema also exhibited passion about something that doesn’t usually elicit such emotions in politics these days: bipartisanship and moderation. Sinema defended the filibuster, which blocks most controversial and major legislation these days, as a tool for moderation. And she said that she views moderation, not passing major changes to election law with just one party, as a means to an end for a healthier democracy.

“When one party need only negotiate with itself, policy will inextricably be pushed from the middle towards the extremes,” she said, adding later: “The past years have shown when a party in control pushes party line changes exceeding their electoral mandate, the bitterness within our politics is exacerbated.”

To make her case, she reached back to 2013, when Democrats ended the filibuster for most presidential nominees. Republicans then took the Senate majority and got rid of the filibuster for Supreme Court nominees and molded the Supreme Court into the most conservative it has been in decades. Now conservatives on the Supreme Court could roll back abortion rights for the first time in 50 years.

Although others would say that all of that was a symptom of polarization, Sinema sees it as the main contributor.

“The impact is clear for all to see, the steady escalation of tit for tat in which each new majority weakens the guardrails of the Senate and excludes input from the other party, furthering resentment and anger among this body and our constituents at home,” she said.

She urged instead that senators listen to each other, and criticized the Democratic Party for not trying to find compromise on voting rights legislation that Republicans could support. “I began my career as a social worker, and in our social work training, our first necessary skill is the ability to listen to others.”

To her critics (which is most of the Democratic Party leaders right now), Sinema will sound wishful, even naive, in her poetic pitch for holding out hope for bipartisanship. President Biden campaigned on a message of unity that is quickly eroding. He signed into law a bipartisan infrastructure bill, but he also recently changed his mind about the filibuster, and this week forcefully said it should be eliminated for voting rights, while likening opponents of making that narrow change to segregationists.

Sinema gave her speech just before Biden arrived on Capitol Hill to lobby her and other senators on getting rid of the filibuster for voting rights.

Sen. Joe Manchin III (W.Va.) is the other Democratic senator who has been preaching bipartisanship. He made a big effort this past year to get Republicans on board with voting rights, but when that failed, he became open to changing the filibuster — but only tweaks that Republicans support.

Sinema’s opposition to eroding the filibuster was practical, too. If Democrats make an exception to the filibuster for any legislation to do with voting rights, what’s to say that Republicans, when they get back in power as early as next year, won’t use it to pass federal voting restrictions? Or weaken it for other specific areas they declare to be of such import?

“Eliminating a 60-vote threshold, on a party line, with the thinnest of possible majorities, to pass these bills that I support will not guarantee that we prevent demagogues from winning office,” she said. “Rather, eliminating the 60-vote threshold will simply guarantee that we lose a critical tool that we need to safeguard our democracy from threats in the years to come.

It’s an argument to which Democratic leaders don’t really have an answer, other than to say that protecting voting rights now is too important not to act.

Sinema somewhat tantalizingly said senators of both parties have offered reforms about the Senate she would support — but she declined to say what. And it’s certainly not weakening the filibuster, even just for voting rights.