President Donald Trump would be better off to challenge special counsel Robert Mueller through legal procedures than to agree to sit down and answer the "open-ended, vague, and general" questions that were revealed this week, Harvard Law professor emeritus Alan Dershowitz said Wednesday.

"Mueller has the ultimate card in his hand, the subpoena card," Dershowitz told Fox News' "America's Newsroom."

You subpoena the president, he has to go in front of the grand jury without his lawyer, without any opportunity to limit the questions."

However, the president can challenge the subpoena through the federal court or even the Supreme Court, where he can argue that a president can't be subpoenaed before a grand jury, said Dershowitz, but he "would possibly lose that."

Trump also could argue that a president can't be asked about why he made certain decisions, or argue that the questions couldn't go beyond the scope of Mueller's authority, particularly about his business dealings, "and he may win or may lose that," said Dershowitz.

But even with all the issues, that would still be better than sitting down and answering Mueller's "list of 40-so odd questions," said Dershowitz.

He added that he did not think the questions, as reported in The New York Times, were well crafted and probably did not come from Mueller himself.

"They were probably just notes taken by the defense team but they certainly show areas of interest," he said. "They show me several things. One, they show that [Deputy Attorney General] Rod Rosenstein must be recused from any further participation in the obstruction of justice part of the case. He is a central witness."

Trump fired FBI Director James Comey, Dershowitz noted, based on a memo from Rosenstein.

"It seems to me these questions put a real onus on Rosenstein to recuse himself," said Dershowitz.

The revealed questions also show there are no limitations about what will be asked, said Dershowitz.

"Plainly they want to ask him questions and give him an opportunity to ramble on and perhaps give them information they don't have, or say things that are contradicted that they do have," said Dershowitz. "One of the reasons they want to haul him in front of a grand jury or ask him questions. They want to see if he is going the lie. It's a perjury trap. It is not the role of a grand jury to set perjury traps. It is to obtain information they don't already have, not to give the subject an opportunity to lie about answers that they do already have."