Earlier this month, a driver illegally parked a Chevy Tahoe in front of the Supreme Court. Capitol Police closed streets and cleared the area. For the next hour, crisis negotiators tried to de-escalate, but the driver refused to talk, saying only that the “time for talking is done.” Finally, police apprehended the unarmed occupant, but even then the authorities couldn’t discern the motorist’s motives.

In this instance, the suspect was a 55-year-old Michigan man. But for those working in the Capitol, the episode might have had a ring of familiarity. For the past couple of months, they’ve been navigating a running standoff with a similarly confounding and inscrutable perpetrator, a 45-year-old Arizona woman. Her name is Sen. Kyrsten Sinema.

The first-term Democrat has parked herself in the middle of the action in the Capitol, blocking legislative traffic and causing gridlock for the Biden agenda. She won’t say what she wants. She won’t say anything, for the most part. And Democratic senators can’t fathom what caused their young colleague’s wheels to spin off in such spectacular fashion.

She and Sen. Joe Manchin III (D-W.Va.) are the two holdouts keeping President Biden’s “Build Back Better” agenda (and with it a $1 trillion infrastructure bill) from passage. But while Manchin has consistent (conservative) positions and has been negotiating in good faith with the White House, Sinema chose this week to fly off to the land of Marie Antoinette.

Yes, Sinema is in Paris — doing a fundraiser, the New York Times reported. The peasants need a child tax credit, Internet access and tuition assistance, and Sinema responds: Qu’ils mangent de la brioche.

Alas, we have seen entirely too much Sinema vérité of late.

President Biden on Sept. 28, continued to meet with lawmakers to urge forward the $1 trillion infrastructure bill and $3.5 trillion spending plan. (Reuters)

During a climactic moment in negotiations a couple of weeks ago, as Biden, the House and Senate desperately tried to reach agreement on the Build Back Better package so the infrastructure bill could pass, Sinema flew home to Arizona — to see a foot doctor, an aide explained. (They don’t have podiatrists in Washington?) It turned out she also attended a spa-resort “retreat” in Phoenix with high-end donors while the frantic negotiations continued in Washington. A few days before that, her fundraising entity held a D.C. event with five corporate lobbying groups at which participants contributed up to $5,800 apiece.

So the entire Biden agenda (not to mention the prospects for a functioning democracy) hangs by a thread because of Sinema, and she’s living her best life, flying to Paris, attending a spa retreat and quaffing wine with corporate donors, many of whom oppose said agenda. Her staff says she’s conducting “remote” legislative negotiations while this is going on. Very remote. Biden, CNN reported, complained to progressives that Sinema didn’t reliably return phone calls from the White House.

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“What Does Kyrsten Sinema Want?” asked Time magazine.

“What, Exactly, Does Kyrsten Sinema Want?” posed Vanity Fair.

“Kyrsten Sinema Is Confounding Her Own Party. But … Why?” questioned FiveThirtyEight.

“Seriously, Kyrsten Sinema, what are you doing?” inquired late night’s Seth Meyers.

What she’s doing is attempting to emulate Sen. John McCain (R-Ariz.), the “maverick” who sometimes defied his own party. But senator, you’re no John McCain. McCain operated from a clear (if occasionally flexible) set of principles. And he always — always — explained himself. Sinema sounds less like McCain than Groucho Marx in “Horse Feathers”:

I don’t know what they have to say.
It makes no difference anyway.
Whatever it is, I’m against it! …
Your proposition may be good,
But let’s have one thing understood:
Whatever it is, I'm against it!
And even when you’ve changed it,
Or condensed it,
I’m against it!

McCain never presided over the Senate in a sweater saying “Dangerous Creature.” Nor did he post an Instagram photo of himself wearing a ring that said “F--- Off.” When McCain gave his dramatic thumbs down on the Senate floor to thwart the GOP’s Obamacare repeal, he did it to reject partisanship. When Sinema repeated the gesture in voting against a minimum-wage increase, it was a symbolic vote signifying — well, it’s not clear. McCain forged coalitions; Sinema blows things up.

Sinema generally avoids reporters’ questions. She’s hardly more forthcoming with colleagues. “Senator Sinema’s position is that she doesn’t negotiate publicly, and I don’t know what that means,” observed Sen. Bernie Sanders (I-Vt.), Budget Committee chairman.

None of it adds up. This former Green Party Naderite is preventing massive investments in climate action. She’s pleasing corporate interests by blocking Build Back Better, in the process killing the infrastructure bill, which business likes. The “Saturday Night Live” version of Sinema explained her this way: “As a wine-drinking, bisexual triathlete, I know what the average American wants.”

Progressive activists have confronted her in person and are warning of a 2024 primary challenge. I suspect neither tactic will work. That’s because the person who poses the greatest threat to the Democrats’ agenda — and the democratic agenda — appears to be dangerously irrational.