NAPLES, Fla. — Former House speaker Newt Gingrich attracted huge crowds in Florida this weekend, but he continued to face down accusations from his rivals that he is too soft on immigration to win the Republican presidential nomination.

Gingrich, 68, who joined former Massachusetts governor Mitt Romney at the top of the field less than two weeks ago, showed no sign of slipping at two appearances along the southwest Florida coast — a conservative enclave and critical battleground in the state’s Jan. 31 primary.

On Friday night, a standing-room-only crowd of at least 800 fans crammed into a hotel ballroom to listen to Gingrich speak. Hundreds who couldn’t fit into the room watched on TV monitors out in the hall.

And on Saturday, at least 500 stood in line for more than four hours at a Books-a-Million bookstore, where Gingrich and his wife, Callista, posed for photos and signed books, t-shirts, photographs and other memorabilia.

The growing energy around Gingrich on the campaign trail may explain why some of his rivals are continuing to go after him on immigration, an issue that surfaced at the most recent televised debate last Tuesday. Gingrich called on Republicans to be “humane” and support a path to legal residency for certain long-time illegal immigrants with deep ties in this country, and since then, two rivals — Romney and U.S. Rep. Michele Bachmann — have attacked Gingrich for what they say is his support for amnesty.

On Saturday, Bachmann repeated her accusation on Fox News claiming that Gingrich has a long record of supporting amnesty for all illegal immigrants, not just those who have been here for decades.

“He would not limit this to people [living here] 25 years,” Bachmann said. “Anyone who is here, he would make legal, that 11 million to 12 million people, overnight.”

Gingrich pushed back forcefully against Bachmann’s comments, telling reporters during his book-signing that he does not support amnesty and did not say he supported amnesty at the debate.

His spokesman, R.C. Hammond, said Bachmann is either “confused or lying,” while Gingrich said: “I’m prepared to talk about substantive change in a number of areas, including Social Security and how we deal with immigration. The American people are prepared to listen to a campaign that deals with substantive issues. Those of my friends who refuse to tell the truth make it harder to do that.”

Nearly all of those who stood in line to hear Gingrich or have their books signed said they did so because he is the smartest candidate seeking the Republican nomination. Many have followed his career in public life for decades, have read his books or watched his documentaries or seen him years ago on C-SPAN, where, early on in his congressional career, he established renown as a conservative commentator.

“There's no hesitancy,” said Pamela Burditt, 48, a pharmacist visiting Florida from Bucyrus, Kansas. “His intelligence is so well-rounded that he doesn’t have to stop and think what his answer will be.”

Gingrich said he was gratified to continue attracting crowds in southwest Florida, a relatively conservative enclave in this enormous state and a critical battleground in Florida’s Jan. 31 primary.

“It’ll be pretty clear by Jan. 31 that I’ll be the conservative candidate in the race,” Gingrich said, adding that he expects the Republican nomination to wind up as a contest between him and Romney.