More than half of all evening television news coverage of the Donald Trump presidency has been dedicated to discussion of the Russia investigation since the appointment of special counsel Robert Mueller on May 17, according to a new study.

The Media Research Center studied every broadcast network evening newscast in the past five weeks and found in a study released Tuesday that 55 percent of all coverage, or 353 minutes of airtime, focused on the ongoing probe into potential ties between President Donald Trump's campaign and the Russian government.

The Russia investigation received 20 times more airtime than the new health care bill, 100 times more airtime than the Trump administration's infrastructure initiatives, and 450 times more airtime than tax reform.

Coverage of the Russia investigation far outstripped any coverage of administration policy moves. Just 47 minutes were spent on the decision to withdraw from the Paris climate accord, 17 minutes were spent on the Republican effort to repeal and replace Obamacare, and only 47 seconds were spent on tax reform initiatives.

The study reviewed 364 evening news stories, covering 640 minutes, focused on Trump or members of his administration. The reports included 246 full stories, 36 anchor-read items, and 82 mentions of the administration. Of these, the Russia story featured in 171 stories—126 full reports, seven anchor-read items, and 38 other mentions.

ABC's "World News Tonight" was number one in Trump-Russia coverage, devoting 63 percent of its Trump news to the topic. CBS's "Evening News" and NBC's "Nightly News" came in with 54 and 48 percent, respectively.

Fifty-eight out of 171 stories, or 34 percent of all coverage of the investigation, were based on anonymous sourcing, the MRC found. Some of those sources later proved erroneous, or were merely speculative. For example, on May 17, CBS correspondent Jeff Pegues reported that "CBS News has learned that investigators believe Flynn may have been acting on orders from someone else."

In one example of poor information from anonymous sources, ABC claimed that an unnamed source had said former FBI Director James Comey was expected in his upcoming congressional testimony to dispute Trump's claim that Comey had told the president three times that he was not under investigation.

"Tonight, a source familiar with Comey's thinking tells ABC News that the former FBI director will directly contradict what the president wrote in the letter telling him he was fired: ‘I greatly appreciate you informing me, on three separate occasions, that I'm not under investigation.' … According to our source, Comey will dispute that," ABC News reporter Jon Karl said.

The next day, Comey said exactly the opposite in his testimony.

Half of all voters think reporters are biased against Trump, according to a recent Rasmussen poll; 68 percent of Republican voters rate the media's coverage as "poor."