Felipe Fernández-Armesto

Normally atop the campus flagpole outside my windows, the Stars and Stripes struggle against the unstable weather. But Tufts University takes seriously its vocation for educating young Americans in global responsibility. Every year on United Nations Day, the flag is replaced with the emblem of the UN.

Last year, it didn't happen - or, rather, the ceremony was transferred to relatively inconspicuous flagpoles nearby. Republican students had unearthed a law that says "No flag shall be substituted for the Flag of the Republic" and threatened to sue the university if the usual routine went ahead. It seemed a typical American incident: rival radicalisms in contention; absurd emotion invested in a bit of bunting; the menace of trigger-happy litigation. I enjoyed it as an amusing jape. It seemed impressive that there were right-wing students at this viscerally liberal place; that they had the self-confidence, initiative and freedom to take on the university establishment; and that they had the wit and cunning to find a law they could use so effectively.

But there was something else going on: something nastier. And it is still going on and getting worse all over the US. Insidiously, the militant Right is organising to change universities, to drive out left-wing personalities, to inhibit criticism and questioning of supposedly American ways of doing things and to warp the curriculum into congruence with the Government's agenda. The trend makes sense in two long-term contexts.

First, the student Right has long fought a formerly honourable, formerly losing battle against the leftward drift. In recent Senate hearings on the nomination of Samuel Alito to the Supreme Court, much was made of Mr Alito's membership of a traditionalist ginger group in his student days at Princeton University, when differences over the admission of women and over the exclusion of army training ended predictably. The disgraced lobbyist Jack Abramoff got his start in politics when he was an undergraduate, organising Brandeis University students in favour of Ronald Reagan's presidential campaign. He did his university a service in shaking up the cosy liberal consensus.

Second, it is fair to say that teachers and students on the left have abused their power and numbers to drown out opinions they dislike.

Political correctness no longer exerts tyranny, but you can see its residual effects on the curriculum - especially in big state universities in liberal states, where some courses seem designed purely as social and political critique or as minority advocacy. Postmodernism is out of fashion, but there are plenty of intellectually corrosive courses around that don't just deconstruct texts but also proscribe facts, outlaw truth and destroy intellectual discrimination. Demonstrators who once shouted down unwelcome or objectionable views invited vengeance. Institutions that ban armed services recruiters from their milk rounds, or stack the course-requirements system against undergraduate cadets, deserve the reproof formerly reserved for other kinds of discrimination.

Now the climate has changed. University trustees are increasingly wary of entrusting their institutions to individuals unsympathetic to the politicians and the voters. The president of Harvard University can question women's vocational aptitude for the sciences and survive in his job. The old left-wing mantras no longer have a talismanic effect. Hip radicalism on campus now looks old-fashioned. Universities can hardly fail to reflect the general shift to the right. Even in Massachusetts, one of the most liberal states, the legislature has voted to deny equality of access to higher education for the children of illegal immigrants.

Right-wing radicals sense the opportunity to exert renewed influence, and to challenge, subvert or reverse the triumph of liberalism in higher education.

They're playing dirty. A controversy at the University of California, Los Angeles has exposed an extreme but not unrepresentative case. A website - uclaprofs.com - professedly run by Republican alumni, names and tries to shame 28 professors who are denounced not for tendentious teaching but for their opinions, expressed outside the classroom in legitimate political activism, or for alleged deficiencies of patriotism, propriety or taste - including personal vanity, moral peccadilloes and opposition to Israel, crudely misrepresented as anti-Semitism. One is even vilified for being the product of a non-elite educational institution. The campaign is candid about its aims: embarrassing the university, alarming the taxpayers and getting the teachers sacked.

Now the operators of the website threaten to obtain evidence of left-wing proselytisation in the classroom by paying student malcontents to act as informers against liberal teachers. The sadness of this is not just that it is vindictive and inquisitorial, but also that it reflects a fundamental misunderstanding of what education is all about. The teacher's freedom of speech is precious not only for its own sake but also because upon it a greater right depends: that of the student to be stimulated into disagreement.

Felipe Fernández-Armesto is Prince of Asturias professor of history at Tufts University in the US.