(CNN) – As some Republicans look for an end to their party's presidential primary, candidate Newt Gingrich said Thursday he continues to campaign because there is no suitable alternative in the Republican field.
"I'm staying in the race because I believe we ought to have a conservative who's serious, who's had national achievements and who doesn't write his policy on an Etch A Sketch and zig-zag back and forth wildly," Gingrich said on CNN's "Piers Morgan Tonight."
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"There may be a morning Governor Romney has a majority of the delegates," he said. "That morning isn't here."
Gingrich argued that his supporters encourage him to remain in the hunt for delegates, which Romney leads by a significant margin. But those wins, Gingrich said, can't be expected in November, when the Republican nominee would face President Barack Obama.
"Every Republican who wants to beat Obama should be worried by the fact the Romney victories come by drowning them out with negative advertising," Gingrich said. "He will not be able to do this to Obama and it makes me worry about what kind of a general election candidate he will be."
Fellow presidential hopeful Ron Paul also disputed on Thursday the notion that a continued primary brawl would hurt the Republican Party.
Romney's buoyancy at the top of the Republican field has come at a heavy price, Gingrich said, as he, Rick Santorum, and Ron Paul "split Romney's attention."
"He has always had an ability to drown us with negative advertising," Gingrich said of Romney. "You'll remember I was actually in first place until we got drowned first in Iowa. Then, I came back and was in first place after winning South Carolina and then they spent $20 million in three weeks in Florida to re-drown me.
"That was the process in which Rick emerged," he said of Santorum, "because he was the guy running fourth, and Romney wasn't paying any attention to him."
At a campaign event Thursday evening, Gingrich acknowledged his "very substantial disagreements" with Romney, but called on his rivals to "all agree that whoever becomes the Republican nominee, we have one common goal and that is to defeat Barack Obama."
Gingrich said that a joke made by actor Robert De Niro at an Obama fundraiser – asking if "our country is ready for a white first lady" – was inappropriate, and that a standard is put on Republicans which is not applied to Democrats. De Niro initially apologized for the joke, and the Obama campaign has distanced itself from the line.
"This campaign isn't about first ladies. I'm not running against Michelle Obama," Gingrich said.
– CNN Political Producer Shawna Shepherd contributed to this report.
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