Special Counsel Robert Mueller's investigation will likely end with some low-level indictments and a report that will not include President Donald Trump, Harvard Law Professor Alan Dershowitz said Saturday.

"[There will be] some indictments and from people who were involved in the campaign or committed crimes, not before the special counsel but because the special counsel was appointed," Dershowitz told Fox News' "Fox and Friends."

"The appointment creates new crimes. Obstruction of justice, tampering with witnesses. That happens all of the time. We end with a report that doesn't include the president."

Further, Trump won't be indicted "because the sitting president can't be indicted," Dershowitz said.

Congress can consider impeachment, he added, noting that in his new book, he makes the argument against impeachment and he hopes that Mueller will read that book before he comes to any conclusions concerning impeachment.

Meanwhile, polls indicate Special Counsel Robert Mueller's approval rating is dropping, and Dershowitz told Fox News the new numbers show what he'd said from the beginning: A special counsel to investigate Russian activities during the 2016 election was never needed.

"An objective, nonpartisan [investigation] would have worked," Dershowitz said. "It's quicker...we don't need to use criminal law as a weapon."

A special counsel investigation is going slowly, "of course," said Dershowitz, as that type of probe goes "for the lowest hanging fruit first. They try to get them to flip. Sometimes they sing. In America, do a crime with someone more important, so they can turn you in. That's how the special counsel works."

Dershowitz said the big picture, overall, is that the 2016 election "was a disaster in every possible way."

"We had efforts by Russia impeding the election," he said. "We had guys up that said let's stop the election of President Trump. We have a big mess. That's why what we needed a commission to make sure this never happens again. Look, I tried to stop the election of President Trump. I voted for Hillary Clinton. I contributed to her campaign. That's the American way. To have a high ranking FBI if I believe trying to stop it creates a lack of credibility in the role of the FBI."

Dershowitz added that he thinks FBI agent Peter Strzok should testify before Congress, but he won't tell the whole story.

"He will answer by saying, 'oh, I was joking, it was pillow talk, It was my girlfriend,'" Dershowitz said of Strzok's anti-Trump messages he exchanged with romantic partner Lisa Page, an FBI lawyer.

"He has to know as an FBI agent there is no such thing as a message that won't become public," Dershowitz added. "For him to say 'I have to stop this [Trump's election] we need a insurance policy,' That sends out such a terrible message about the role of the FBI in American politics. The public just won't accept that. We want clean elections. "