It was a restrained, PG-rated debate in a primary campaign drenched in vulgarity and rhetorical bile. But in the last forum before the critical primaries in Florida and Ohio, the Republican presidential contenders all gave powerful signals of where their candidacies are headed.

For Donald J. Trump, the debate on Thursday was an acute test of his fluency with policy. For Senator Ted Cruz of Texas, it was an opportunity to set the rules of engagement that might govern a drawn-out nomination fight between him and Mr. Trump.

And for Senator Marco Rubio of Florida and Gov. John Kasich of Ohio, it was a last chance to appeal for loyalty and support from the states that elevated them to high offices — and that have the power to sustain or break their campaigns on Tuesday.

Trump repudiated Republican policy

Under determined questioning, Mr. Trump was finally forced to fill in some of the gaping blanks in his policy vision. The result was a broad rejection of core Republican priorities. He assailed free-trade agreements, pledged not to cut government benefits for retirees and defended taking a neutral stance in negotiations with Israel and the Palestinian Authority.