Officials in Hawaii have certified Obama’s citizenship, but "birthers" have demanded additional proof. And Trump, who is weighing whether to seek the Republican presidential nomination, says not all the questions haven’t been answered.

In an interview broadcast today, Trump told NBC News he plans to decide by June whether to run, and said that if he is the GOP nominee, "I’d like to beat him straight up," not on the basis of the question of where Obama was born.

Trump insisted he didn’t introduce the citizenship issue, but he isn’t letting go of it either. Since he was asked about it during an interview several weeks ago, the real estate executive said, he’s looked into it and now believes "there is a big possibility" Obama may have violated the Constitution.

"I’d like to have him show his birth certificate," Trump said. "And to be honest with you, I hope he can."

Asked in the interview how genuine his presidential ambition is, Trump said, "I always take things seriously, but I’ve never taken it seriously like this. I wish I didn’t have to do it."

"I wish this was the greatest place in the world," Trump said. But he said the United States is losing respect in the world at a time when jobs at home are vanishing. He accused Obama of giving the country "a terrible presidency."

Trump said that if the current fight over budget issues forces a shutdown, "I think the president will be blamed."

He accused Obama of conducting a confusing policy on the civil war in Libya, saying "nobody knows what’s happening, and now it looks like (Libyan strongman Moammar) Gadhafi is going to beat the United States."

"I’m only interested in Libya if we get the oil," Trump said. He said Obama "doesn’t have a doctrine (on foreign affairs.) Foreign affairs is, we take care of ourselves first"

Of Obama, he said, "I want him to do well. … I love this country, but this country is going to hell. … The world laughs at us. They won’t be laughing if I’m elected president."