Representative Claudia Tenney, a first-term Republican from Central New York, said in a radio interview on Wednesday that “so many” mass murderers “end up being Democrats.”

Democrats immediately condemned her remarks, which came a week after 17 people were killed at a high school in Parkland, Fla., and called on her to apologize for politicizing gun tragedies.

One of Ms. Tenney’s colleagues in the House, Representative Gerry Connolly, a Democrat of Virginia, wrote on Twitter that she “owes America a sincere and abject apology.” And her expected Democratic challenger this year, State Assemblyman Anthony Brindisi, said in his own Twitter post that her “toxic rhetoric” was “a new low” and that “inserting politics into a national tragedy is beyond the pale & disgusting.”