Republican candidates for US president agreed that Iran must not develop atomic weapons even if a tactical nuclear strike is needed to stop it and accused Democrats of being soft on the issue.
The front-runners for the Republican Party nomination in the November 2008 election also squabbled among themselves over a broad immigration overhaul being debated by the US Congress.
The gentlemanly debate featured small policy differences on a host of issues, and even electrical glitches caused by lightning, but no big gaffes or disputes that could immediately change the political dynamic in the closely fought Republican battle.
In a debate in New Hampshire where the country's first primary will be held next year, they were largely in agreement on an issue that President George W Bush considers vital -- preventing Tehran from developing nuclear weapons.
Iran insists its nuclear program is for civilian use only, but the West is deeply skeptical and is trying to resolve the problem through diplomacy.
"You shouldn't take any options off the table," said the leader in the Republican pack, former New York Mayor Rudolph Giuliani, when asked whether a tactical nuclear strike might be necessary.
Democratic candidates had their own debate in New Hampshire on Sunday and largely agreed the United States should open direct diplomatic talks with Iran on the nuclear issue. Giuliani said it sounded to him like "Democrats were back in the 1990s."
A second-tier candidate, California Rep. Duncan Hunter, was more direct, saying the United States reserved the right to dissuade Iran militarily.
"I would authorize the use of tactical nuclear weapons if there was no other way to preempt those particular centrifuges," he said, while noting it could probably be done with conventional weapons.
But Texas Rep. Ron Paul, a candidate drawing about 2 percent in opinion polls, opposed a nuclear strike on moral grounds and because he believed Iran was no threat to US national security.
"We, in the past, have always declared war in defense of our liberties or go to aid somebody," Paul said. "But now we have accepted the principle of preemptive war. We have rejected the just war theory of Christianity."
The Republican candidates showed impatience with the direction of the Iraq war. Some said if a US troop buildup ordered by Mr Bush did not show solid progress by September, a plan should be developed to split Iraq into Sunni, Shia and Kurdish states.
Arizona Sen. John McCain, who is risking his political future by backing the Iraq war when most Americans are tired of it, was the biggest supporter of the troop buildup among the candidates, saying Iraq would become a haven for terrorists if US troops left too early.
The debate featured 10 Republican candidates, all white men.