What is the definition of a moderate? It appears to be someone who agrees with you all the time. How else to fathom the progressive vitriol against Susan Collins?

As the Senate wraps up Donald Trump’s trial, Maine’s senior senator has been called a fake, a “mythological” moderate, a tool of Mitch McConnell.

Her liberal votes (there have been many) have been ascribed to political calculation. Her conservative votes (also many) are said to prove that Collins, who opposed Trump in 2016, has become his “servant,” his “loyalist,” his “sycophant.”

This seems unfair. Since Trump took power, Collins has voted with and against him. She has declared her openness to a subpoena of Trump’s tax returns and stated that Russia’s interference in the 2016 election was real.

In the run-up to the impeachment trial, she predicted she would vote to elicit “more information.” She sided mostly with her party, but not entirely.

Critically, and unlike McConnell, who said conviction is “inconceivable,” Collins said she would not prejudge the case. She said the Senate should weigh the facts first.

This should be Collins’ moment. She has been likened, with tiresome frequency, to her independent-minded predecessor, Margaret Chase Smith. As a freshman senator in 1950, Smith made a gutsy speech condemning the Red-baiting tactics of fellow Republican Joseph McCarthy.

Smith was celebrated, ultimately across the political spectrum, for her courage. Collins’ ratings are dropping like a stone. In a recent poll, Collins, who faces re-election in November, was ranked the most unpopular sitting senator. Her opponents say she has changed. We all do, but the times have changed more.

During Smith’s Eisenhower-era heyday, moderation was respected. We seem to have passed through a time warp. The present age more recalls that of New England’s greatest senator, Daniel Webster.

In 1850, to head off a threatened secession, Webster — one of the trio of 19th-century senatorial giants — promoted a compromise with the slave states. It was a bad bargain, toughening the Fugitive Slave Law. Webster’s former supporters never forgave him, and his career was ruined.

The devil in Collins’ case was her vote to confirm Trump’s second Supreme Court nominee, Brett Kavanaugh. It made her the progressives’ target. By comparison, you hardly hear of their venom for Ted Cruz, one of the most conservative senators ever.

But it is a bad time to be a moderate. An extremist abhors a moderate, because they present a reasonable alternative.

Moderates have positions, extremists have crusades. Disagreement becomes a deviation, akin to betrayal.

It is possible to cherry-pick votes from Collins’ career to make her look extreme. But in a fair weighting, she deserves her reputation as center right on a (shifting) spectrum.

She is a longtime supporter of abortion rights, reasonably liberal on immigration, fiscally conservative — though she deviated on the Trump tax cut — mixed on guns. She initially voted against Obamacare, then provided a crucial vote against Trump’s bid to repeal it.

The common thread is that Collins is an institutionalist. Like Webster, she tilts against upheaval. She voted for most of Trump’s judges, and for most of Obama’s. Her default is to confirm. She is skeptical of the mob, especially a censorious mob. She tailors passions to procedure — perhaps overly. She not only confirmed Kavanaugh, but also acquitted, in his trial, Bill Clinton. If she had a natural political party, it might be that of Whig, the pro-commerce and progressive elitist party of its time. Webster was its champion.

Collins consistently scores at the top of the charts for bipartisanship. The Lugar Center and Georgetown University ranked her the most bipartisan senator for three straight Congresses. During Trump’s tenure, according to FiveThirtyEight, McConnell voted with Trump 94 percent of the time. Chuck Schumer, minority leader, voted Trump’s way 23.5 percent of the time. Collins was squarely between them: 67 percent.

Many of Collins’ positions were controversial. She backed Trump’s decision to fire FBI Director James Comey but spoke in favor of protecting Special Counsel Robert Mueller. She opposed Trump’s temporary ban on immigration from seven Muslim states.

The curse of our age is to impugn to disagreement unclean motive. This allegation of insincerity rankles Collins. In the trial, she protested the Democrats’ incivility. The rub is, they have the evidence. Trump abused his power — none has refuted it. Collins’ stock in trade is to call them as she sees ’em. Her call on this one will determine her legacy.