WASHINGTON (Reuters) - U.S. Deputy Attorney General Rod Rosenstein on Wednesday dismissed Republican lawmakers’ charges that government attorneys and agents investigating allegations of Russian interference in the 2016 election are biased against President Donald Trump.

Republicans have attacked Special Counsel Robert Mueller, who has charged four Trump associates in his investigation, which is also looking into possible collusion between the Trump campaign and Moscow officials.

Testifying before the U.S. House of Representatives Judiciary Committee on Wednesday, Rosenstein said he was “not aware” of any impropriety by Mueller’s team.

When the committee’s ranking Democrat asked if he had any good cause for firing Mueller, he replied: “No.”

Russia denies the conclusions by three U.S. intelligence agencies that Moscow used hacking and disinformation to affect the election, and Trump says there was no collusion.

At the hearing, Republicans on the committee increased their criticism of Mueller, highlighting text messages between two Federal Bureau of Investigation employees, including an agent on his investigating team, as evidence of bias against Trump.

So far, however, congressional Republicans have stopped short of calling on Trump to fire Mueller.

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Republicans said they had reviewed more than 300 anti-Trump text messages exchanged last year between FBI lawyer Lisa Page and Peter Strzok, an FBI agent who worked on Mueller’s probe.

Members of the committee read aloud the contents of some of the text messages between Strzok and Page.

Some texts call Trump an “idiot” and a “loathsome human,” according to copies of a sampling of the texts reviewed by Reuters.

In one July 2016 exchange they poked fun at Trump’s campaign during the Republican National Convention.

“My god, I’m so embarrassed for them. These are like second-run stars,” Page responded to Strzok. “And wow, Donald Trump is an enormous d*uche.”

The texts showed “extreme bias against President Trump, a fact that would be bad enough if it weren’t for the fact that these two individuals were employed as part of the Mueller ‘dream team’ investigating the very person for whom they were showing disdain,” said Bob Goodlatte, the Republican chairman of the Judiciary Committee.

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In some of the texts seen by Reuters, however, Strzok did not seem excited about Democratic Presidential candidate Hillary Clinton, either.

Describing himself as a “conservative Democrat,” he in one text openly worried about her getting elected, and at one point complained that certain news media outlets were biased for downplaying her ties to the oil and gas industry.

“This is clear and utter bias by the media specifically the NYTIMES, WAPO, and CNN who if you look at all of them have large donors for Clinton,” he wrote.

Rosenstein, who appointed Mueller, said the special counsel properly removed Strzok from the probe after the Justice Department inspector general brought the texts to light, and added he was confident Mueller is not letting political bias color the investigation.

He also said he thinks Mueller is the “ideal choice” to lead the investigation, and said that just because a person is affiliated with a political party does not mean he or she will be biased.

He said he had discussed the issue of bias with Mueller and that Mueller “is running that office appropriately.”