Harvard Law School professor Alan Dershowitz on Saturday dismissed a major argument Democrats have been making against Donald Trump Jr., and said it's clearly unconstitutional.

Several Democrats have argued that U.S. election laws prevent campaigns from receiving anything of "value" from foreign entities, and have said in Congress and in television interviews that items of "value" can be more than money, and can also be information.

That, Democrats say, is why President Trump's campaign violated election laws when Donald Trump Jr. met with a Russian lawyer who said she had dirt on Hillary Clinton.

But in an interview that aired Saturday night on Fox News, Dershowitz said campaign finance laws have never been prosecuted that way. He also said using the law to prosecute people who obtain information from non-U.S. sources would violate the First Amendment.

"Under the campaign finance laws, I mean, there is a claim that if you get something of value, and they're alleging that information... from a foreign national could be, you know, stretched out to mean, you know, words," Fox News host Jeanine Pirro said Saturday night. "Is that's something that's ever been prosecuted?"

"Of course not, and if it were to be prosecuted, the First Amendment would trump," Dershowitz replied. "A candidate has a right to get information from whatever source the information comes."

Dershowitz went on to say that just as newspapers are free to print any information they obtain from others, even when the source obtains it illegally, candidates for office have the same right to get information anywhere they want.

He also stressed again there is no legal precedent to treat information as money under U.S. campaign finance laws.

"You can't include information under the campaign finance law," he said. "That would be unconstitutional."