President Trump responded Wednesday to the news that former special counsel Robert Mueller will testify publicly next month, saying, "Well my reaction is it never ends."

The president made the comments on Fox Business' "Mornings with Maria Bartiromo," launching into his frustrations and claims of vindication over the Russia investigation.

Mueller will testify in open session July 17 before the House Judiciary Committee and House Intelligence Committee after Democrats subpoenaed him to appear. Intelligence Committee Chairman Adam Schiff said Mueller was "very reluctant" to appear before the committees.

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On Wednesday, Mr. Trump claimed that Mueller "obviously was not a Trump fan, not a Trump person."

"It's hard to have obstruction when you have no crime," the president said. "How many time do we have to go through with this?"

The president later claimed that Democrats are "fighting so hard because they think the 'real stuff' is going to be revealed" during a public hearing.

Later Wednesday, Mr. Trump heads to Japan for the Group of 20 summit, where he is expected to meet with Chinese President Xi Jinping and other world leaders. The president said he thinks the two nations can make a trade deal, but at the same time he's happy with where things are, claiming the U.S. is taking in a "fortune" from China through tariffs. Mr. Trump said he's happy "either way" with a deal or without one.

On the flight to Osaka, Mr. Trump told Bartiromo that he would begrudgingly watch the first 2020 Democratic debate. He predicted that while it will be "very boring" to watch, "I have to watch it, it's a part of my life now."

"Do I want to watch these people? It's a very unexciting group of people," Mr. Trump said of the presidential contenders.