Americans are so focused on the outrageous presidential candidacy of Donald Trump, we've largely missed one of the biggest political stories of 2016: the left's fearsome tactics to suppress its ideological opponents. Case in point: the liberal crusade to silence climate change dissenters.

About 20 Democratic attorneys general have launched a campaign to go after ExxonMobil and other "corporate polluters" for allegedly disseminating "false" information about global warming. What did the Democratic Party do? Mock this campaign? No. Denounce it? Nope. Tell them to knock it off? Of course not. Instead, the Dems made this stance an official plank in their party platform, pledging to use the "Department of Justice to investigate alleged corporate fraud on the part of fossil fuel companies who have reportedly misled shareholders and the public on the scientific reality of climate change."

Eco-warriors claim to have internal memos that prove that ExxonMobil knew as far back as 1977, well before global warming achieved any sense of true public urgency, that doubling atmospheric carbon dioxide would produce a 2 to 3 degrees centigrade rise in global temperature. Liberals also claim that the company internally debated the impact of warming on its Arctic operations as far back as the early 1990s. But just like tobacco companies kept publicly denying the link between smoking and lung cancer even though they knew the truth, Exxon spent $30 million over the years to fund global warming "denialism" and stop action on climate change.

These claims are overblown at best.

First of all, comparing tobacco to fossil fuels is not just absurd, but malicious, given that smoking actually directly kills smokers. Now before you argue that global warming might one day kill people too, remember that fossil fuel is a source of cheap power without which countless millions of poor people, especially in Third World countries, would perish here and now, not in some distant future when the Earth heats up.

As for those so-called smoking gun memos, they were mere speculations that repeatedly and correctly emphasized the deep uncertainties in climate science at the time. And when the Intergovernmental Panel on Climate Change definitively declared in 2006 that the observed warming had human causes, my Reason colleague Ron Bailey has reported, ExxonMobil started warning investors that both climate change and the policies it spawned posed a risk to its business. It also switched from opposing climate change action to supporting a carbon tax.

But none of this matters to global warming warriors who, in a zeal reminiscent of the great Spanish Inquisition, want to jail climate dissenters and have marked Exxon for "corporate death." To achieve that end, they are colluding with the Democratic Party and going after Exxon and any group that has had anything to do with climate change.

Last fall, a bunch of climate scientists at George Mason University dashed off a letter pressing the Justice Department to use the anti-mafia racketeering law called the RICO Act to investigate Exxon's alleged conspiracy of deceit. And instead of rejecting the suggestion outright, Attorney General Loretta Lynch referred the issue to the FBI, which is ominous enough.

Worse, this spring, some state attorneys general who are members of "AGs United for Clean Power" issued subpoenas to Exxon for all communication since 1977 with about 100 think tanks, advocacy groups, lobbyists, and university centers that it has funded (including Reason Foundation, where I work, which received funding from Exxon many moons ago). They also held a press conference — with none other than Al Gore to add a touch of objectivity, no doubt — announcing their intention to get to the bottom of Exxon's conspiracy.

But the First Amendment protects all corporate lobbying — even deceptive corporate lobbying. As such, this legal jihad is unlikely to result in charges. So what is its purpose? To harass Exxon to the point that it ends donations to outfits whose research and policy advocacy these AGs find threatening. When the Competitive Enterprise Institute, one of the listed groups, pointed out this gross abuse of power in an opinion piece, Claude Walker, the attorney general of the Virgin Islands, slapped it with a separate subpoena, demanding all correspondence with Exxon from 1997 to 2007.

Corporations usually succumb in the face of government harassment to avoid costly discovery and bad publicity. But this campaign is so beyond the pale that Exxon actually hinted that it would countersue and also filed for declaratory relief in a Texas district court on grounds that its constitutionally protected rights to free speech and due process, and against illegal searches and seizures, were being violated. Meanwhile, CEI filed a motion for sanctions against Walker, which would force him to pay its legal fees and possibly other damages. And the Energy and Environment Legal Institute, a free market legal group, FOIAed the emails of the so-called independent George Mason scientists who masterminded the missive to the Justice Department and has found clear evidence of not just collusion between them, various attorney generals, and other Democratic lawmakers, but also an effort to deceive reporters about it.

Such damning revelations have caused Walker — along with the attorneys general of Massachusetts and California — to back off. The only holdout in their cabal is New York's AG Eric Schneiderman, but he's playing a losing hand.

Still, this victory for constitutional liberties will be short lived if Hillary Clinton becomes president, given that the Democratic Party has officially declared its intention to continue to wage this war to silence climate change dissenters.

This is why it would behoove the GOP to put all of this centerstage in this election.

That would of course require a sane nominee interested less in himself and more in the Constitution. But Trump is so busy threatening even worse First Amendment violations to settle his own personal vendettas — for example, by threatening anti-trust action against Jeff Bezos, The Washington Post owner, for running "wrong" stories about him — that he has neither the interest nor the standing to expose the excesses of his political opponents.

Even if he loses, which, god willing, he will, this election will have been a huge missed opportunity to expose and moderate the agenda of the left. As things are shaping up in this awful campaign, regardless of what happens in November, free speech rights are in for a fight of their life in this country.