Sen. Cory Booker (left) and Sen. Kamala Harris listen to testimony from Christine Blasey Ford during a Senate Judiciary Committee hearing, September 27, 2018. (Tom Williams/Pool via Reuters)

Democrats turn impartial fact-finding into taxpayer-funded opposition research.

The Left ruins everything.

That’s because the Left stands ready to eradicate any norm at any time if there is political advantage in it. The latest to be cast aside are the precepts that we never tolerate unbridled, abusive investigations, nor do we abide full-blown criminal investigations without solid evidence that a crime has been committed — and even then, we demand adherence to time-honored limits.

In the probes of Donald Trump and, now, Brett Kavanaugh, these norms have been wiped away by the simple expedient of rebranding criminal investigations. Now the sleuths are unleashed under the guise of “counterintelligence” and “background checks” — whatever pretext is needed to get their foot in the door. Once they’re in, the earth is to be scorched, as if the crime of the century had occurred.

Of course, we want criminal investigators to be aggressive. But that has always meant aggressive within strict parameters. These are dictated by the degree of certainty that a crime has been committed, and by due-process rules with which the FBI must comply or be held to account when the case gets to court.

By contrast, when the Left criminalizes political opposition, no crime is required; just gossamer-thin, incoherent, uncorroborated, often unverifiable allegations: perhaps multiple-hearsay innuendo against a Republican presidential candidate, passed on by anonymous foreigners to a hyper-partisan, left-wing foreign spy working for the opposition Democratic political campaign. Or maybe a 36-year-old claim of sexual assault by an alleged victim who cannot remember basic details or keep straight the details she claims to remember; whose named witnesses do not back her account; who declines to address whether her accusation has been influenced by the controversial psychotherapeutic process of “recovered memory”; who refuses to disclose highly relevant therapy notes and polygraph information; and who is a Democrat advised by a prominent Democratic strategist and represented for free by Democratic activist lawyers, who were recommended to her by a senior Senate Judiciary Committee Democrat even as that Democratic senator concealed the sexual-assault claim from her Republican counterparts.

The Left requires no solid evidence of a crime, because solid evidence — the kind that truly justifies a criminal probe — narrows a good-faith investigator’s focus. To the contrary, the Left wants all the aggressiveness of a criminal investigation but none of the limits. The criminalization of politics leans on counterintelligence and background investigations; it wants no part of criminal courts, where due-process safeguards are enforced and allegations must be proved.

Political progressives will tell you this is just “good government” in action. Republican presidents and their appointees may not technically be criminal suspects, but they must be investigated as if they were, in order to protect our institutions.

In reality, this is the antithesis of good government. It is an ugly process in which the new Democratic party — the party that prefers Bill Ayers to Joe Lieberman, “social justice” to patriotism, and “change” to the Constitution — menaces decent people and their attachments to American traditions until they retreat from the public square.

The world has changed. People who care nothing about norms can no longer be dismissed as a fringe. For generations, left-wing activists have instructed students and other groups that norms are the building blocks of a rigged system that deprives them of power and denies their “selfless” desires.

We don’t want to acknowledge what this has wrought. We have norms because they safeguard foundational principles, such as due process, the presumption of innocence, and freedom from unreasonable and unwarranted police prying. But the Left is no longer attached to those principles. Far from protecting what we must preserve, norms are seen as the redoubts of adversaries who must be not merely defeated but humiliated. Defeat is fine for the enemy at hand, but humiliation is what suppresses prospective challengers. Would you put your family through what the Kavanaugh family has been put through?

Under the pretext of carrying out its counterintelligence mission or conducting a background check, the Left turns the FBI loose to do an aggressive investigation that leaves no stone unturned. Except now there is no crime — no proper trigger, no identifiable criminal transaction with essential elements on which the FBI can get a quick, definitive handle. Instead, the bureau is being told to leave no stone unturned until it finds something on which the president can be impeached. Democrats demand that Judge Kavanaugh’s life be scrutinized until the FBI finds some misconduct — no matter how old, ambiguous, and remote from his developed adult character — that might be used to brand him unfit for the High Court.

Counterintelligence is not an excuse to subject someone to what is actually an aggressive criminal investigation in the absence of a known crime. A background investigation is not an occasion for a deep dive into every nook and cranny of a person’s life, much less for a full-blown criminal investigation, as if the person were on trial. A background check is just an exercise in gathering enough information so that we can judge whether a person is a good fit for the responsibilities of an office. If a Democratic senator has already decided against a conservative nominee over philosophical differences about abortion and gun rights, the senator should simply vote against the nominee, not exploit a background check as an abusive fishing expedition.

The Left is destroying investigative norms. If we do not insist on these norms and defend them, then investigations become a political weapon from which only the Left will be spared. The moral of the story: When politics is involved, we can no longer presume that investigations are being sought and will be conducted in good faith. We should not agree to them in the absence of enforceable norms that limit scope, protect privacy, and ensure that decent people of all ideological persuasions are not discouraged from participating in the political life of a free, pluralistic society.