In Republican Debate, Ted Cruz and Marco Rubio Wage Urgent Attacks on Donald Trump

Senators Marco Rubio and Ted Cruz, fighting for their political lives, relentlessly demeaned and denounced Donald J. Trump at Thursday’s debate, all but pleading with Republicans to reconsider nominating a candidate with a long history of business failures, deep ties to the Democratic Party and a taste for personal insults.

Warning that Mr. Trump would lead the party to a historic defeat in November, Mr. Rubio and Mr. Cruz delivered their attacks with urgency, as if trying to awaken voters who had fallen under Mr. Trump’s spell. Mr. Rubio derided Mr. Trump

as untrustworthy and uncivil, while Mr. Cruz bashed him for donating money to Hillary Clinton’s 2008 presidential campaign and to other Democrats.

But the debate in Detroit also deteriorated at times into the kind of junior high school taunts that have startled many Republican elders but done little to dent Mr. Trump’s broad appeal. At one point, as Mr. Trump and Mr. Rubio traded insults over their manhood, Mr. Trump recalled Mr. Rubio’s innuendo that Mr. Trump’s “small hands” correlated with another part of his anatomy.

Mr. Trump, who has boasted about his sexual exploits, insisted that nothing was small about him. “I guarantee you,” Mr. Trump continued with little subtlety, “there’s no problem. I guarantee you.”

The two senators repeatedly urged Republicans to align against Mr. Trump in nominating contests over the next two weeks, saying that Mr. Trump could sew up the nomination even though a majority of voters so far have cast ballots for other candidates.

“Two-thirds of the people who cast a vote in a Republican primary or caucus have voted against you,” Mr. Rubio told Mr. Trump. “The reason why is because we are not going to turn over the conservative movement or the party of Lincoln or Reagan, for example, to someone whose positions are not conservative.”

The pleas reflected not only Mr. Trump’s advantage in the race, but also the party’s growing disquiet about the implications of nominating him. The specter of Mr. Trump as the Republican standard-bearer has long troubled both establishment-aligned and conservative leaders. But his initial hesitation to condemn the Ku Klux Klan in an interview on Sunday, and his success in seven stateson Super Tuesday, has set off a new wave of anxiety that Mr. Trump could tarnish the party this year and perhaps beyond. And it has prompted leading Republicans to acknowledge that the 2016 campaign may result in an irreparable breach not seen in the party for over a century.