Mitt Romney chugged ahead Thursday as the conservative-fueled drive to deny him the Republican presidential nomination reached a difficult new phase: Once-surging rivals Rick Perry and Herman Cain scrambled to control serious damage, while an old face sought new ways to exploit their problems.

Former House Speaker Newt Gingrich could emerge as the newest hope for conservative activists who doubt Romney’s commitment to their priorities. But Gingrich trails Romney and others in organizing in key states such as Iowa. And he will have to prove that his long and sometimes troubled political history can withstand closer scrutiny.

Meanwhile, Texas Gov. Perry rearranged his schedule Thursday to try to mitigate a disastrous debate moment, in which he could not remember the third federal agency he has vowed to abolish. Perry canceled a Tennessee fundraiser to appear on several TV networks and the David Letterman show, pledging to stay in the race.

He repeatedly said he “stepped in it” at the Wednesday night debate but declared in an interview, “This ain’t a day for quitting nothing.”

For Cain, the former pizza company executive, it was day 11 of trying to get beyond sexual harassment accusations leveled against him by four women, two of whom received cash settlements from a trade association Cain once headed.

Facing voters for the first time since the allegations emerged, Cain met with tea party groups in Michigan, hoping the friendly settings would preserve the lofty perch he enjoyed in GOP polls two weeks ago.

Romney, the former Massachusetts governor, filmed a TV ad in Iowa on Thursday and blasted President Barack Obama’s Iran policy in a Wall Street Journal opinion piece. His supporters quietly reveled in the good fortune of Perry’s and Cain’s woes.