Sen. Susan Collins at the U.S. Capitol in October. Associated Press/J. Scott Applewhite

Back in 2016, long before the world as we knew it turned upside down, Sen. Susan Collins spoke to me with passion and eloquence about what being a Republican meant to her.

“Five generations of my family have served in public office as Republicans,” she said at the time. “This is part of my DNA.”

She was explaining what had prompted her to say in her memorable op-ed in The Washington Post that then-candidate Donald Trump was “unworthy of being our president.” That she could not support him, even as he sat atop her party’s ticket, because he was so antithetical to all Republicans stood for.

“Being a Republican,” she explained to the nation, “is part of what defines me as a person.”

Now, with the U.S. Capitol scarred by rioters and Trump’s presidency in tatters, Maine’s senior senator has a choice to make – and not just whether she will vote to convict Trump on the article of impeachment that the House of Representatives passed Wednesday.

No, Collins must decide which Republican Party she wants to belong to.

Will it be the party of her own heritage – conservative, yes, but also rooted in civility, personal responsibility and, above all, sanity?

Or will it be the party of Trump – unhinged, violent and propelled by mob rule?

She can no longer have it both ways. The chasm is too vast to straddle.

Last week, as momentum built toward a second Trump impeachment following the attack by his supporters on the beating heart of our democracy, Collins said through her spokeswoman that she would not be commenting on the impeachment “because of the Senate’s constitutional role in those proceedings, which includes sitting as a jury.”

It’s the same line Collins used this time last year, when she kept mum right up until she voted against convicting Trump because of what she perceived as a lack of sufficient evidence.

She tried to placate her critics then by saying Trump had learned “a pretty big lesson” from that impeachment. She implied that, going forward, he’d somehow tone down his scattershot of assaults on the nation he was elected to lead.

Fast forward through a tragically botched response to the COVID-19 pandemic, a re-election campaign built on lies, a post-election period roiled by the Biggest Lie – that the election was “stolen” – and finally an incitement to sedition that led to a riot. Collins’ rose-colored glasses notwithstanding, the only lesson Trump learned was that he wasn’t being offensive enough.

So, here we go again. Of the four members of Maine’s congressional delegation, Reps. Chellie Pingree and Jared Golden already have voted to impeach. Sen. Angus King has announced that, short of removing Trump from office by some other means, he will vote to convict.

And Collins, elevating political caution to the theater of the absurd, still considers herself an impartial juror, duty bound to keep her thoughts to herself while 20,000 National Guard troops take up positions across the nation’s capital.

A juror?

Senator, you were an eyewitness.

Beyond that, you were a potential victim. When those MAGA-festooned insurrectionists stormed the Capitol nine days ago, they weren’t just raising hell. They were coming after lawmakers like you.

In an op-ed for the Bangor Daily News on Monday, Collins wrote of struggling to flee in her high heels even as the seditionists took over the Senate Chamber behind her.

“My first thought,” she recalled, “was that the Iranians had followed through on their threat to strike the Capitol.”

Granted, none of us can control the thoughts that sometimes pop into our heads. But embedded in that single line is the startlingly distorted prism through which Collins apparently sees this moment in history.

She had witnessed the Trumpsters already massing on her way into the Capitol that day. Yet, when the order to evacuate came only two hours later, her first thought was … the Iranians?

How could Collins, like everyone else, not know instantly who was behind this unprecedented attack?

Was it because they were a tableau of middle-class, white America and, however upset they might be, middle-class, white Americans simply don’t participate in such anarchy?

Was it because when it comes to attacks on our country, we reflexively look outward at foreign invaders rather than inward at ourselves?

Was it because Trump, the man she helped keep in office a year ago, is a Republican and his supporters are Republicans and Republicans, of all people, would never smash windows, kick in doors and erect gallows, complete with a noose, just outside the Capitol?

Was it because Republicans don’t kill a U.S. Capitol police officer with a fire extinguisher?

When she sided against tossing Trump last February, Collins at least had the matter of her re-election to consider, much as she did all last year as she steadfastly refused to say whether she planned to vote for Trump come November.

But she herself won another a six-year term in that same election. There is no longer any political risk to standing up and being counted, to sending a signal to her constituents and fellow Republican senators that this is a bridge too far, that Trump, even at this late hour, has to go.

Her good friend Sen. Lisa Murkowski, R-Alaska, in whose home Collins took refuge that dark night, last week called on Trump to resign immediately.

At the same time, Murkowski, who defied far-right Republicans by winning re-election as a write-in candidate in 2010, said that “if the Republican Party has become nothing more than the party of Trump, I sincerely question whether this is the party for me.”

That same choice now confronts Collins.

There are no more opportunities for her to hedge. Her country exploded before her very eyes last week and, from Washington, D.C., all the way to Augusta, there are real fears that it could happen again.

Her lofty detachment as a member of the “jury” belies the glaring fact that she already knows what happened, she saw what happened and, most importantly, she saw who instigated it.

What is left to decide?

The whole world is watching, Senator Collins.

So are four generations of your forebears.