Leftist protesters are making violence and intimidation a regular feature of the American public discourse.

Ferguson. Baltimore. Chicago. Everywhere Leftist protesters occupy the streets, those whose opinions are deemed insufficiently progressive are abused, mocked, ridiculed, brutalized and physically menaced. This lawlessness is rapidly becoming the norm; the Obama administration, as well as leading media and cultural figures, need to decry that normalization and act strongly against these thugs now – before the American public square is transformed beyond recognition, and ceases to be an arena for free discourse.

Although this violence and brutalization of political opponents is a new phenomenon in American politics, it has a historical antecedent: the Nazi Brownshirts. In The Coming of the Third Reich, historian Richard J. Evans explains how, in the early days of National Socialist Germany, Stormtroopers (Brownshirts) “organized campaigns against unwanted professors in the local newspapers [and] staged mass disruptions of their lectures.”

To express dissent from Nazi positions became a matter of taking one’s life into one’s hands. The idea of people of opposing viewpoints airing their disagreements in a civil and mutually respectful manner was gone. One was a Nazi, or one was silent (and fearful).

That is just the kind of public arena that the Left has been trying to bring to the United States for years. For decades, they have told us that their political and ideological opponents are not just wrong, but malevolent. In college in the early 1980s, I was taken aback by the obscene, relentless, vicious hatred that the Left directed toward Ronald Reagan – I was at that time entirely sympathetic with their disdain for him, but the frenzy with which they expressed it, their wild furious contempt, shocked me.

And that was nothing compared to what they had in store for George W. Bush. Years ago, the Democratic Party as a whole, along with the entire Leftist establishment, adopted the Alinskyite tactic of ridiculing, mocking and smearing their foes instead of engaging them on the level of ideas. Leftists today routinely portray their opponents as simultaneously stupid and evil, idiotic but crafty; it’s practically a reflex.

The shutdown of Trump’s rally in Chicago, however, takes this one step farther. Trump supporters leaving the arena in Chicago after the Left-fascists had forced cancellation of the Trump rally last Friday experienced that firsthand. AP reported that “the protesters closed in on the building, obstructing most of the exits just as Trump supporters began filing out. The Trump supporters had little choice but to push through the anti-Trump crowds that parted only slightly, yelling, ‘Racists go home!’…Trump supporter Bill Vail said he walked through a gauntlet of protesters who cursed at him as he pushed through holding his 9-year-old daughter’s hand. She cried, he said.”

Commented Vail: “They scream about tolerance, but are being intolerant themselves. That doesn’t make sense.” Yes, it does. Clearly the authoritarian, America-hating Left has decided that the Brownshirts had a good idea: those whose dare to oppose their political views will henceforth be greeted with truncheon and fist. Soon the dissenters will learn their lesson, and accept the Left’s agenda with docility.

Cruz, Rubio and Kasich are already learning to do this, as they demonstrated when they had the audacity, or craven opportunism, to claim that Trump’s rhetoric was at least partially responsible for the shutdown of the Chicago rally. Do they think they will be spared? Do they realize that by charging that Trump bears partial responsibility for the thugs’ actions, they have tacitly validated those actions, implying that under some circumstances, the forcible shutdown of one’s political opponents was acceptable – if, say, that political opponent was prone to saying “outrageous” things?

They don’t realize that once that premise has been accepted, it can be turned on them. And it will be. Now that they’ve apparently agreed that violent thugs can be justified in forcibly silencing those they hate, what will they possibly say when the thugs decide that they, too, have strayed beyond the bounds of what one is allowed to say?

Cruz, Rubio, and Kasich – to say nothing of Clinton, Sanders, and Obama – should have forcefully and unequivocally condemned the Chicago thugs, called for their arrest, and declared their unshakeable support for civility in the public discourse and respect for one’s ideological opponents. Instead, they all contributed to the erosion of that civility and respect, and took the U.S. just a bit closer to becoming a tyranny in which the goons who shut down politically unacceptable rallies work for the state.

Hitler and Himmler and Goebbels, if they’re able to look on from their fiery graves, may be feeling a sense of having, at long last, triumphed.