Maine’s Republican Sen. Susan Collins has done a lot to make her state proud. Often, she has stood her centrist ground against the howling winds of partisanship, and her even-keeled approach has made her something of a rarity in Washington.

Most recently, she served as the GOP’s voice of reason on the Senate floor, proposing a gun control compromise that would block those on two government watch lists from buying firearms.

Now, it’s time for her to step up again — this time to say that she will not endorse her party’s presumptive nominee, Donald Trump.

According to a report in Politco, Collins was “still evaluating” her position on Trump when the candidate was in Bangor Wednesday.

At this point, what’s left to evaluate? There’s no need to wait to see if Trump is going to appear more presidential — for months we’ve endured his racist, misogynistic outbursts and outright lies.

It doesn’t matter if he learns to stay on script. Trump showed his true colors from Day 1, after descending the escalator of his gilded tower to present Mexicans as killers and rapists and to propose a border wall with no clear execution.

He hasn’t changed since.

Trump’s sins, gaffes and promises make him unfit for office, including:

• Proposing to ban all Muslims from entering the U.S. and falsely claiming thousands in New Jersey celebrated the destruction of the Twin Towers;

• A laundry list of personal insults and below-the-belt strikes leveled against political opponents, including the claim that Ted Cruz’s father “was with Lee Harvey Oswald” before the JFK assassination;

• Unwarranted attacks on journalists, including an instance where he appeared to mock a reporter’s disability;

• Mocking Sen. John McCain’s status as a former prisoner of war;

• Encouraging violence at his rallies.

Strip all that away, though, and you’re left with a businessman plagued by multiple bankruptcies and failed ventures who has never held elective office and is woefully uninformed on U.S. policy.

So what’s a Senator to do? Collins could instead endorse either Hillary Clinton or a third-party candidate, though neither scenario seems likely.

We appreciate that Collins must be careful with who she backs for president. But in the case of Trump, the best course is to back away. Far away.