Republican Sen. Chuck Grassley on Thursday said he supports the release of the Mueller report.

Trump initially seemed open to having the report released, but now opposes making it public.

Grassley is the President pro tempore of the Senate, making him the second highest-ranking official in the chamber and t hird in line to succeed to the presidency.

Republican Sen. Chuck Grassley and President Donald Trump are at odds this week.

Grassley, a veteran GOP senator with significant influence in Congress, on Thursday went against Trump in a big way and said he supports the release of special counsel Robert Mueller's report on Russian election interference.

"I support release of the Mueller report," Grassley said in a tweet on Thursday morning.

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Grassley is the President pro tempore of the Senate, making him the second highest-ranking official in the chamber and third in line to succeed to the presidency after the vice president and House Speaker. He's also a senator from Iowa, the site of the first major presidential nominating contest.

The Republican senator's comments on the Mueller report come a day after he referred to Trump as "idiotic" for suggesting wind turbines cause cancer.

Earlier this week, Trump said those calling for the full report to be released are a "disgrace."

Initially, Trump appeared to support making the report public. "Let it come out. Let people see it — that's up to the attorney general," the president said in late March.

The report is hundreds of pages long, but so far the public has only seen a four-page summary from Barr and congressional Democrats are pushing for its release.

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Barr's summary said Mueller did not find evidence of collusion between the Trump campaign and Russia, adding that the special counsel did not conclude Trump committed obstruction of justice but also did not fully exonerate the president, either.

Polls have repeatedly shown that a majority of Americans would like to see the Mueller report released.