U.S. Special Counsel Robert Mueller makes a statement on his investigation into Russian interference in the 2016 U.S. presidential election at the Justice Department in Washington, May 29, 2019.
U.S. Special Counsel Robert Mueller makes a statement on his investigation into Russian interference in the 2016 U.S. presidential election at the Justice Department in Washington, May 29, 2019.

U.S. President Donald Trump blasted former special counsel Robert Mueller, who agreed to provide open testimony before congressional committees next month.

"The Mueller thing never stops," Trump said on the White House South Lawn before his departure to the G-20 summit in Osaka, Japan. "How many times do we have to hear it? It never ends," Trump said, adding his often-repeated line of no obstruction and blaming the Democrats for "criminal activities," calling it "the greatest hoax ever in the history of our country."

The chairmen of the U.S. House Judiciary Committee and the House Intelligence Committee, Rep. Jerrold Nadler and Rep. Adam Schiff, announced in a letter late Tuesday that Mueller would appear July 17, and that they and all Americans looked forward to hearing from him.

Mueller led a nearly two-year investigation into Russian interference in the 2016 election and allegations that Trump obstructed justice by trying to shut down the probe.

FILE - Rep. Jerrold Nadler, D-N.Y., center, flanked by Senate Minority Leader Chuck Schumer, D-N.Y., left, and Rep. Adam Schiff, D-Calif., speaks on Capitol Hill in Washington, June 14, 2018.

He issued a report, a redacted version of which was made public in April, that concluded the Trump campaign had not colluded with Russia during the election, but reached no conclusion on the question of obstruction of justice.

Trump has been highly critical of the process, repeatedly calling the investigation a "witch hunt."  His reaction shortly after Tuesday's announcement came in the form of a tweet: "Presidential Harassment!"

Mueller's only public comments to this point have been at a news conference in May during which he read a prepared statement, but took no questions.

Nadler and Schiff had issued subpoenas seeking to compel Mueller to testify, explaining that while they noted the special counsel's desire for his written report to stand on its own, the public deserves to hear directly about not only his conclusions but also the investigation itself.

"Americans have demanded to hear directly from the special counsel so they can understand what he and his team examined, uncovered, and determined about Russia's attack on our democracy, the Trump campaign's acceptance and use of that help, and President Trump and his associates' obstruction of the investigation into the attack," Nadler and Schiff said in their letter Monday.

House Democrats have sought not only the release of more of the information from the Mueller report, but have also continued to seek testimony from White House and Trump campaign officials to learn more about what took place during the election and the first portion of Trump's term in office. Republicans have criticized the ongoing investigations, saying Congress needs to move on.

Rep. Doug Collins, the top Republican on the House Judiciary Committee, said he hopes Mueller's appearance "marks an end to the political gamesmanship that Judiciary Democrats have pursued at great cost to taxpayers."

"May this testimony bring to House Democrats the closure that the rest of America has enjoyed for months, and may it enable them to return to the business of legislating," Collins said in a statement.

House Speaker Nancy Pelosi welcomed Mueller's testimony, citing concerns about the next election and saying lawmakers have a "patriotic duty to follow the facts, so we can protect our democracy."

"The Mueller Report revealed that the Russians waged a 'sweeping and systematic' attack on our elections, and America's top intelligence and law enforcement officials have warned that the Russians will attack our elections again," she said in a statement.  "Yet, sadly the President calls it a hoax, and suggests that he would welcome Russian interference again."