Romney has hit Huckabee over the same issue, as well as for breaking from the Republican establishment in other ways. On Tuesday, he attacked Huckabee over a published comment apparently made in jest that President Bush did not read the annual National Intelligence Estimate "for four years."
"This is not a time to be mocking our president, and it was, I think, in bad taste," Romney said in Johnston, a Des Moines suburb. "I think that we should come together and recognize the great work our president is doing and not take our rhetoric or our plays from the Democratic playbook."
Huckabee responded to attacks on his credentials as a fiscal conservative with a new television ad saying that as Arkansas governor he had signed the state's first broad-based tax cut in 160 years.
He also released a new ad underscoring his opposition to abortion rights.
The two former governors also continued to draw on Huckabee's unusual news conference Monday.
Before a roomful of reporters and TV cameras, Huckabee announced that he would not air an advertisement he had just produced attacking Romney, but then showed the ad to the assembled news media.
The move raised questions about whether Huckabee was attempting to lead reporters to carry negative messages about Romney in a way that allowed him to assert that he was running a positive campaign.
Huckabee did not mention Romney by name during his midday appearances Tuesday but appeared with a banner that read, "Enough Is Enough," which was the title of the ad he had canceled.
Huckabee found himself on the defensive with reporters who questioned whether his continued use of the slogan was disingenuous.
"It's still valid," Huckabee said. "Enough is enough of the negative campaigning. . . . The Tonya Harding school of politics has to stop."
Romney sought to keep the issue alive.
"It does remind you a bit of a person who stands up and says, 'I'm not going to call my opponent any names, but here are the names I'd call him if I were going to call him names,' " Romney said. "What he did yesterday didn't fool the media, and I don't think it will fool the people of Iowa either."
The splintering in the GOP field has occurred in part because voters have come to believe that the leading candidates each have a different strength, the Times/Bloomberg poll found, with no one candidate dominating on a wide range of leadership qualities.
Romney was seen in the poll as best equipped to handle economic issues. Huckabee was strong on social issues in Iowa -- but not in New Hampshire, where the moderate wing of the party is stronger. McCain is seen as the best equipped to handle foreign affairs.
Among Democrats, by contrast, a single candidate -- Hillary Rodham Clinton -- dominated in all those policy areas, the poll found.
Ken Khachigian, a California-based GOP political strategist, sees the intraparty fragmentation as a reflection, in part, of modern politics' tendency to focus on narrow constituencies rather than big-picture themes the way Reagan did.
"He understood the poetry of politics," Khachigian said. "That's the big difference this year -- we are losing the poetry for narrowcasting."
Khachigian and other Republicans argue that in the end, Clinton may prove the great unifier of the GOP. If she wins the Democratic nomination, they say, Republicans of all stripes will rally in their shared loathing of her.
"Hillary, for Republicans, is the gift that keeps on giving," said Dirk Van Dongen, a business lobbyist who supports Giuliani.
But an effort built around beating Clinton would not amount to the kind of grand, idea-driven campaign that conservatives aspire to, Newhouse said. "That would be for winning an election, not for maintaining a governing majority."
Times staff writers Joe Mathews and Scott Martelle contributed to this report.