WASHINGTON — Last fall, Donald J. Trump inadvertently touched off a national conversation about sexual harassment when a recording of him boasting about groping women was made public at the same time a succession of women came forward to assert that groping was something he did more than talk about.

A year later, after a wave of harassment claims against powerful men in entertainment, politics, the arts and the news media, the discussion has come full circle with President Trump criticizing the latest politician exposed for sexual misconduct even as he continues to deny any of the accusations against him.

In this case, Mr. Trump focused his Twitter-fueled mockery on a Democratic senator while largely avoiding a similar condemnation of a Republican Senate candidate facing far more allegations. The turn in the political dialogue threatened to transform a moment of cleansing debate about sexual harassment into another weapon in the war between the political parties, led by the president himself.

Indeed, Republicans on Friday were more than happy to talk about Senator Al Franken, Democrat of Minnesota, who apologized this week after a radio newscaster said he forcibly kissed her and posed for a photograph a decade ago appearing to fondle her breasts while she was sleeping. Democrats, for their part, sought to keep the focus on Roy S. Moore, the Republican candidate in Alabama who has been accused of unwanted sexual conduct by multiple women going back even further, including one who was 14 at the time.