As conservatives fought against cancel culture on college campuses, they developed a particular fondness for the First Amendment. It was un-American, they argued, to punish someone for exercising their right to speak freely.

Today, however, many of those same conservatives, now in power in state and federal government, are behind a growing crackdown on political expression at universities, in ways that try to sidestep the Constitution’s free-speech guarantees.

President Trump and Republican lawmakers say that new laws and policies are necessary to protect students from harmful and objectionable content, to prevent harassment and to discourage conformity.

To that end, Mr. Trump has threatened to withhold hundreds of millions of federal dollars from universities because they moved too slowly to quell protests that left many Jewish students feeling threatened. And Republicans in state legislatures have drafted sweeping prohibitions against classroom “indoctrination” and the display of certain L.G.B.T.Q. symbols. They have also demanded the removal of art they consider inappropriate.

In some cases, the Trump administration has said existing federal law already gives the president all the power he needs to act. When Mr. Trump said he would deport student activists, for example, he claimed to be acting in the interest of American foreign policy.

Tellingly, administration officials have said they are not bound by the First Amendment when it comes to noncitizens.