Former House speaker Newt Gingrich (R-Ga.) said Thursday that he expects Texas Gov. Rick Perry’s decision to drop out of the White House race and endorse his bid will be “very helpful” to his campaign.

“It’s another step,” Gingrich told PBS’s Gwen Ifill in an interview that will air Thursday night, according to an early excerpt. “I think, frankly, when Michele Bachmann stepped out, when Herman Cain stepped out, at each stage — and even a little bit with Tim Pawlenty — at each stage you began to see conservatives who would not go to Romney because he was just too liberal for their background.”

“And so, I think that Governor Perry actually endorsing me today was very helpful and I think will make a very big difference both around the country and an enormous difference in Texas,” he added.

Asked whether he thought former senator Rick Santorum (R-Pa.) should drop out of the race — as Gingrich earlier suggested he should — the former House speaker said that Santorum “has every right” to stay in the race.

“Well, Rick Santorum has to do what he wants to,” Gingrich said. “But people, after all, said back in June and July that I was dead, and I didn’t stop. So Rick has every right to keep running. He just, after all, was declared the winner in Iowa.”

Gingrich noted, however, that he plans to make “a very direct appeal” for Santorum’s backers.

“If you look at the polling numbers, I am the only candidate who could potentially stop Mitt Romney,” he said. “And so voters who don’t want a Massachusetts moderate — or, by the standard of most Republicans, a liberal — I’m the only practical vote in order to stop him.”

The interview comes hours ahead of a key debate and two days before the GOP’s first-in-the-South primary in South Carolina, where Gingrich is hoping for a strong showing — even as he contends with the decision by his former wife, Marianne Gingrich, to go public with the private details of her 18-year marriage to the candidate.