Over the last three decades, Americans have witnessed the gradual erosion of our civility and maturity due to corrosive politics. If you’ve ever wondered what it would look like when we hit rock bottom, now we know. We’re there.

And it was, of all things, the debate over an infrastructure bill that took us to the bottom.

I would have put my chips on guns, abortion, or immigration. When did fixing roads, repairing bridges and modernizing airports get to be so controversial? It was probably around Election Day 2020, when Joe Biden was elected president as a moderate despite opposition from progressives, and then he proceeded to govern by attempting to please both factions.

Biden, who has been in politics since 1973, should have known better. Trying to make everyone happy only makes everyone angry.

So what does rock bottom in our political discourse look like? It looks like left-wing protesters harassing Democratic Sen. Kyrsten Sinema of Arizona on Sunday and chasing her into a bathroom stall at Arizona State University, where the freshmen senator has taught since 2003.

The entire sophomoric episode was — naturally — videotaped and posted on social media. The zealots probably thought they were embarrassing Sinema; they have no idea that the joke is on them.

Over the sound of flushing toilets, an activist identified as “Blanca” can be heard scolding Sinema through the closed door of the stall.

A group of activists had actually ambushed Sinema as she exited her classroom, but the senator refused to engage with them. “Actually, I’m heading out,” she told them before retreating into the bathroom.

That was a mistake. Sinema should have met with the activists and heard them out. She’s a public servant, and a state university is a public institution. I assume these protesters pay taxes, and thus foot the bill for Sinema’s salary — and one day, her gold-plated congressional pension.

But that she refused to meet with the activists is still no excuse for stalking a U.S. senator, haranguing her like a child, videotaping the whole affair and then — in a spate of cyberbullying — posting the video online.

On Monday, Sinema jabbed back at the activists. “Yesterday’s behavior was not legitimate protest,” Sinema said in a statement. She called the ambush “unacceptable” and accused the agitators of engaging in “unlawful activities” such as “disrupting learning environments.”

The youthful protestors — who identified themselves as belonging to a Latino group that calls itself “Living United for Change in Arizona” (LUCHA) — supposedly got in Sinema’s face to hold her accountable for not delivering on her promise to support immigration reform.

Don’t believe it. Many Democratic elected officials make that same promise. Like Sinema, they don’t deliver. But because they’re Democrats, Latinos give them a pass.

This spectacle was not about immigration but infrastructure. It was about Sinema’s steadfast refusal — along with fellow moderate, Democratic Sen. Joe Manchin of West Virginia — to support a massive $3.5 trillion infrastructure package that wouldn’t merely fix roads, bridges and airports but also pay for health care, child care and combating climate change.

The protesters showed their cards. The video footage shows the group chanting “Build back better!” and “Pass the bill!”

Last week, Manchin announced that his spending limit for the budget reconciliation package is $1.5 trillion. The West Virginian said he doesn’t want to contribute to an “entitlement mentality” among Americans. Sinema seems to be in line with that lower figure as well.

At this point, it appears unlikely that the progressives will get the whole enchilada. They would be wise to try to negotiate with the two holdouts instead of insulting and demonizing them.

For the life of me, I can’t figure out what terrible sins Manchin and Sinema have committed. They’re doing what they think is right, and they’re trying to represent their conservative constituents in red or purple states that can be difficult for Democrats to hold. This sort of thing comes with the territory when a party tries to broaden its electorate, win more votes and turn itself into a big tent.

Hey Democrats, remember when you used to drone on incessantly about the virtue of diversity? You said we shouldn’t just tolerate each other’s differences but celebrate them. You were insufferable, as you constantly presented yourself as more enlightened and “woke” than the rest of us.

Well, guess what? This is diversity. Not of race, ethnicity, gender or sexual orientation. This is diversity of thought and opinion. Isn’t it grand?

Ruben Navarrette’s email address is ruben@rubennavarrette.com.