Without uttering a word to students at the University of California, Berkeley, Ann Coulter on Wednesday made herself the latest cause célèbre in the rapidly escalating effort by conservatives to fight liberals on what was once the left’s moral high ground over free speech on campus.

Ms. Coulter, the acid-penned conservative writer, canceled a planned appearance on Thursday after the political organizations that invited her rescinded their support over fears of violence. “It’s a sad day for free speech,” she said.

But across the country, conservatives like her are eagerly throwing themselves into volatile situations like the one in Berkeley, emboldened by a backlash over what many Americans see as excessive political correctness, a president who has gleefully taken up their fight, and liberals they accuse of trying to censor any idea they disagree with.