Donald Trump said Sunday that he is continuing to think about running for president in 2016, and that he would use his fortune to fund the effort.

Asked about his current net worth, Trump said it is "probably over $10 billion."

"If I made a decision (to run), I'd spend a lot," Trump said on ABC's "This Week". "If I did it, I'd spend whatever it took."

Forbes recently estimated Trump's net worth at $3.2 billion, but Trump said his business ventures have done increasingly well over the last year.

As the conversation turned to his potential candidacy, though, Trump made clear he's not done raising concerns about whether President Obama was actually born in the United States.

"Some people say that was not his birth certificate. I'm saying I don't know," Trump said. "Nobody knows. And you don't know either, Jonathan. You're a smart guy, and you don't know."

When the interviewer, Jonathan Karl, responded that he was "pretty sure" the document Obama produced was legitimate, Trump pounced.

"'Pretty?' Aaah! Pretty? Pretty?" Trump responded.

Karl then stated that he was "totally, without question" convinced that Obama was a natural-born citizen.

"Let's just see what happens over time," Trump said, adding that he didn't think Karl was actually 100 percent sure.