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



