"'Shut up,' he explained." That's a sentence from Ring Lardner's short story "The Young Immigrunts." It's an exasperated father's response from the driver's seat to his child's question, "Are you lost, Daddy?"

They also can be taken as the emblematic response of today's liberals to anyone questioning their certitudes. As with the father in the story, it's a response that indicates uneasy apprehension — the fear that they have no good answer.

It was not always so. Today's liberals, like those of Lardner's day, pride themselves on their critical minds, their openness to new and unfamiliar ideas, their tolerance of diversity and differences. But often that characterization seems as defunct as Lardner, who died far too young in 1935.

Consider the proliferation of speech codes at our colleges and universities. The website of the Foundation for Individual Rights in Education sets out the speech codes at 400 of the nation's largest and most prestigious institutions of higher learning. The liberals who run these institutions — you won't find many non-liberals among their faculties and administrations — have decided to limit their students' First Amendment right of freedom of speech.

One would have thought that universities would be the last place to limit free speech. The American Association of University Professors was founded a century ago this year precisely to champion free speech on campus.

That was then and this is now. We are told that speech codes are necessary because some students may be offended by what others say. In recent years we have been warned that seemingly innocuous phrases may be "micro-aggressions" which must be stamped out and that "trigger warnings" should be administered to warn students of possibly upsetting material.

Sadly, students join in on the fun. They demonstrate to block speeches on campus of people such as George Will, Condoleezza Rice and IMF head Christine Lagarde. They musn't let any dissenting voices or dissident ideas be heard! This is liberalism at work in America today.

Fortunately, there are dissenters. FIRE has brought successful lawsuits against some codes and has persuaded some universities to drop their codes. The University of Chicago recently issued a strong statement supporting free speech on campus. So did former Chicago adjunct law instructor Barack Obama.

But colleges and universities remain largely no-go territory for those who disagree with prevailing campus opinions. A notable exception is Liberty University, founded by the Rev. Jerry Falwell, whose mostly conservative students in great numbers listened politely and attentively to a speech by presidential candidate Bernie Sanders. It was quite a contrast with places like Harvard.

Even beyond the campus, liberals are eager to restrict free speech. This is apparent in some responses to those who argue that global warming may not be as inevitable and harmful as most liberals believe, and that while increased carbon emissions would surely raise temperatures if they were the only factor affecting climate, some other factors just might be involved.

Many liberals won't hear of this — and don't want anyone else to, either. Some extremists call for global warming "deniers" (a word used to suggest kinship with those who deny the Holocaust occurred) to be imprisoned or even executed as heretics. Democratic Sen. Sheldon Whitehouse has called for criminal investigation of global warming theory critics under the federal anti-racketeering statutes.

Whitehouse is not the only Democratic senator who is determined to stamp out the free speech of those who disagree with him. In September 2014, 54 Democratic senators voted to amend the First Amendment of the Constitution to allow Congress and state legislatures to set "reasonable" limits on how much candidates can raise and spend during their campaigns and how much individuals and corporations could spend to influence elections.

This was an attempt to overturn the 2010 Supreme Court decision in Citizens United v. FEC, which Barack Obama denounced a few weeks later in his 2010 State of the Union message and which Hillary Clinton has been denouncing in debates and on the stump. The case involved government efforts to bar distribution of a movie critical of Clinton during the 2008 campaign.

When Justice Alito asked the deputy solicitor general whether the government could ban a book that expressly backed or opposed a candidate, the answer, after some uncomfortable stammering, was yes, they could.

In the 1930s liberals expressed outrage over Nazi book burnings in Germany. Today, liberals' response to opposition is that of Lardner's lost parent: "Shut up," they explain.

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JWR contributor Michael Barone is senior political analyst for The Washington Examiner.