Harvard University professor Alan Dershowitz alleged Friday that Media Matters has "crossed the line into anti-semitism" by tolerating an employee who uses charged language to criticize supporters of Israel.

Dershowitz, a liberal Democrat who is a staunch supporter of Israel, first started speaking out against the liberal media watchdog group last month. He went further in an interview on Fox News, saying Friday that Media Matters has crossed the line into "bigotry."

The professor directed his complaints at one staffer in particular, M.J. Rosenberg, for downplaying the Iranian nuclear threat and repeatedly employing the term "Israel firster" -- an epithet that implies somebody's loyalties are to Israel before America.

"When you accuse Jews of dual loyalty, you invoke a canard that goes back hundreds of years and falls into the category of anti-semitism," Dershowitz said. "To the extent that Media Matters hired him to do that and is tolerating him, they have crossed the line into anti-semitism."

Dershowitz called on Media Matters to fire Rosenberg, but also called on the White House to disassociate itself from Media Matters -- warning that their cozy relationship would cause problems in the 2012 reelection campaign.

"The president should do to Media Matters what he did to Jeremiah Wright -- totally disassociate, rebuke and say 'I stand with Israel,'" he said.

Rosenberg, a senior foreign policy fellow, often writes about the heated rhetoric in Washington regarding the possibility of a conflict with Iran over its nuclear program. He is a sharp critic of Israeli Prime Minister Benjamin Netanyahu and has been warning the U.S. against joining his administration in any military campaign against Iran.

Rosenberg is hardly alone in those opinions, but his critics complain he also resorts to name-calling in the course of making his arguments.

In a column last month, Rosenberg argued that the "Israel firster" term is "accurate," if not polite, in covering the issue of a possible war with Iran.

"There is no need here to describe who the Israel Firsters are. They are those people (of whatever ethnic background) who invariably support Israel's policies over those of the United States," he wrote.

Dershowitz, though, argued that Israel's and America's interests are aligned, and said Rosenberg was effectively accusing people like him of "treason."

"It's the oldest of charges ... accusing Jews of dual loyalty, and it can't be tolerated, whether it comes from the left or the right," he said. "The tent is not big enough to include people who have engaged in bigotry against the Jewish people."

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