Exclusive: Donald Trump Says It 'Could Be' That Some Undocumented Immigrants Stay

— -- In an interview with ABC News' David Muir, Donald Trump refused to say if undocumented immigrants who don’t necessarily want to become citizens would have to leave the country, admitting the possibility that they could stay.

When asked if some of the 11 million undocumented immigrants could stay, Trump replied, "It could be but what’s going to happen is if you’re going to be a citizen, you’re going to leave and you're going to have to come back."

Muir followed up, asking about undocumented immigrants who did not want to become citizens of the U.S.

"They have to make a determination what happens when the border is secure," Trump said.

"So you’re open to them staying here undocumented?" Muir asked.

"I’m going to make a decision, or somebody will. Whether it’s me or somebody else because by that time we’ll have a secure border, we’ll have a wall," Trump said.

To catch David Muir's interview with Donald Trump and Mike Pence, watch "Good Morning America" at 7 a.m. Tuesday.

But, despite a hardline immigration speech last week, Trump admitted that he still grapples with the thought of deporting families whose children are U.S. citizens. Muir invoked comments made by top supporter Rudy Guiliani who said on Sunday during an interview with CNN that Trump "would find it very, very difficult to throw out a family that has been here for 15 years and they have three children, two of whom are citizens. That is not the kind of America he wants."

When asked about Giuliani's comments, Trump responded, "He’s 100% right. It’s very difficult. It’s a very difficult thing to do."

During his speech in Phoenix last Wednesday, he was emphatic in declaring that all undocumented immigrants would have to leave.

"There will be no amnesty. Our message to the world will be this: You cannot obtain legal status or become a citizen of the United States by illegally entering our country,” he said then. "Under my administration anyone who illegally crosses the border will be detained until they are removed out of our country and back to the country from which they came."

Trump also made conflicting statements earlier on Monday during a press gaggle aboard his plane, on the issue of undocumented immigrants achieving legal status.

Initially, when asked what he would do with undocumented immigrants in the country, Trump said, “I’m not ruling anything out.”

A reporter asked if that includes a path to legal status.

"No. To become a citizen you’re going to have to go out and come back. Through the process you’re going to have to get on line. This isn’t touch back,” Trump replied.

However, when asked again about a path to legal status, Trump responded, "We’re going to make that decision into the future.”

But during that speech in Phoenix, Trump adopted a tougher tone.

"For those here illegally today who are seeking legal status, they will have one route and one route only: to return home and reply for reentry like everybody else under the rules of the new legal immigration system,” Trump said.

Immigration, though considered Trump's hallmark issue after he rose to fame proclaiming that he would build a wall on the border with Mexico, is one of the issues on which Trump perhaps has fluctuated the most. Prior to his immigration speech, he indicated in an interview that there would be a "softening" of his immigration plan, surveying a Fox News town hall audience on which stance he should take.