Define “absolutely unacceptable.”

That was the phrase appropriately chosen by U.S. Sen. Susan Collins on Monday to describe Donald Trump’s latest descent into the darkness that was once Collins’ Republican Party.

Still, the question lingers: What is Collins going to do about it?

Trump’s claim – that the judge presiding over the Trump University fraud case has a built-in conflict of interest because he’s of Mexican heritage and Trump wants to build a wall between the United States and Mexico – is by no means his first major stumble on the road to the Republican nomination in Cleveland next month. Nor, undoubtedly, will it be his last.

But with each gaffe (Trump heaped more fuel on the fire Sunday by speculating that a Muslim judge also would be conflicted by Trump’s proposed ban on Muslims entering the country), you’ve got to wonder how someone like Collins still manages to drag herself out of bed each morning.

Granted, she’s not quite in the same political pickle as, say, House Speaker Paul Ryan, who now finds himself calling Trump’s words “the textbook definition of a racist comment” less than a week after Ryan reluctantly endorsed The Donald for president.

Unlike so many of her colleagues on Capitol Hill, Collins has yet to endorse Trump outright. Instead, she’s said repeatedly that she’ll wait until after the convention to express her presidential preference, that she hopes Trump will clean up his act between now and then, and that she expects, as usual, to support her party heading into the general election.

Now this.

“Donald Trump’s comments on the ethnic heritage and religion of judges are absolutely unacceptable,” Collins said in a written statement. “His statement that Judge (Gonzalo) Curiel could not rule fairly because of his Mexican heritage does not represent our American values. Mr. Trump’s comments demonstrate both a lack of respect for the judicial system and the principle of separation of powers.”

Well said, senator. So well, in fact, that to follow such a clear assessment with down-the-road support for Trump as the nation’s next chief executive would represent the height of hypocrisy – not to mention direct complicity in installing a wack job in the White House.

Collins’ unwillingness to loudly, clearly and permanently disavow Trump sooner rather than later appears rooted in two guiding principles for Maine’s senior senator.

The first is an abiding loyalty to her party.

The second is that when that party appears fractured, the best way to maintain broad support is to remain as noncommittal as possible for as long as the political winds will allow.

Both strategies have served Collins well in the past.

Neither will now.

The party to which she’s devoted her entire adult life is on the brink of collapse.

Seeing the faces of “establishment” Republican leaders these days, as they literally sweat through the latest round of Trump aftershocks, is like watching the flight crew of a jumbo jet after the entire control panel suddenly goes dead. They know they eventually have to land this baby, but they haven’t a clue how they’re going to do it.

As for keeping the base happy, or at least on board, the simple reality for Collins and the few remaining centrist Republicans like her is that this is no longer just another topsy-turvy general election year. It’s a hijacking.

Meaning Collins can’t win.

Her old-school loyalists, if they dare speak up at all, wonder wistfully what’s become of the civility and true conservatism on which they once hoisted the Grand Old Party banner.

The newcomers in the bright red “Make America Great Again” hats, meanwhile, already denounce Collins – whether she backs Trump or not – as a RINO (Republican In Name Only) who’s as bad as the damned Democrats, maybe worse.

“I have news for you Ms Collins ‘We The PEOPLE’ are weary of your kind and no longer have much respect for you or the judges or the lawyers that are part and parcel of the problem in this country,” one reader commented on Tuesday’s Press Herald story on Collins’ remarks. “Even if he is not the ideal candidate, Mr Trump is a breath of fresh air in the stale halls of government. … He speaks for many of us.”

Thus, for all her hedging, Collins has little to gain and a lot to lose by clinging to the delusion, as she implied Tuesday, that all of this is still fixable.

“I do believe in redemption, and I hope that Trump will change,” she said in an interview on WGAN Newsradio.

And what if he does “change”?

Do we then excuse all that he’s said to date as the manipulative hype of a reality TV huckster?

Or are we now past the point of no return? Despite his belated efforts Tuesday to backpedal in the judge brouhaha, is it finally time, in the never-ending offensive that is Donald Trump, to pick a side?

Collins herself acknowledged Tuesday that Trump’s comments about Judge Curiel “are of a different magnitude” and that “this is discouraging because it is so serious in what it says about his world view.”

What it says – and Collins knows this as well as anyone – is that Trump is the Republican Party’s worst nightmare. And it’s high time the party that spawned him, if it’s serious about its future, began standing up to him and stopped quietly enabling him.

South Carolina Republican Sen. Lindsey Graham never has stood taller than when he told MSNBC on Tuesday that he could not, and would not, support Trump from this point forward.

“A lot of people want to be loyal to the Republican Party, including me,” Graham said. “But there will come a point in time where we’re going to have to understand that it’s not just about the 2016 race. It’s about the future of our party. I would like to support our nominee – I just can’t.”

See that, Sen. Collins? A loyal Republican, from the Deep South, no less, just announced in no uncertain terms that he’s had it with Donald Trump. And he urged other Republicans to do the same.

To do anything less at this point? To continue to treat this not as a moral imperative but as a political calculation?

That would be absolutely unacceptable.