(Bloomberg) -- Robert Mueller will appear grudgingly before House committees this month, but the former special prosecutor’s testimony is the best chance Democrats have to revive their stymied probes of President Donald Trump.House Speaker Nancy Pelosi’s resistance to a politically risky impeachment inquiry leaves six committees pursuing Trump-related inquiries without a clear mission. And a White House order that current and former officials refuse to testify, or limit their testimony, has deprived Democrats of big-name witnesses.It’s a predicament that has left lawmakers frustrated and has driven some to sarcasm. “As we speak, I have three people in the basement training on how to work the rack,” said Representative Gerald Connolly of Virginia. “And I’ve got another team that is expert, I am told, at pulling off fingernails."So House Democrats are banking on the made-for-TV spectacle of Mueller testifying on July 17 at a morning session of the Judiciary Committee and an afternoon meeting of the Intelligence Committee. Yet Mueller, who agreed to show up under subpoena, has made clear that he has no intention of going beyond the report he issued in April on his 22-month probe into Russian interference in the 2016 presidential election.“Robert Mueller is being asked to testify again,” Trump tweeted on Tuesday. “He said he could only stick to the Report, & that is what he would and must do.”But Judiciary Chairman Jerrold Nadler of New York said Mueller’s testimony could have “a profound impact,” if he simply gets the American public to focus on what he said in his 448-page report. Mueller said he couldn’t conclude whether Trump’s campaign conspired in Russia’s election meddling -- and that he couldn’t exonerate Trump from attempting to obstruct his probe.Risk of Letdown“It’s a big deal. But it also could be a big letdown,” Samuel Everett Dewey, a former congressional lawyer who led investigations in key committees in both the House and Senate, said of Mueller’s testimony.Dewey said the high-profile event would backfire for Democrats if it becomes another in a series of anti-climactic episodes in their probes. Promises of public hearings have vaporized into canceled testimony and empty witness chairs, or acquiescence to closed-door interviews with ground rules set by the administration.Lawmakers will break for a six-week summer recess from Washington a week after Mueller testifies. If they find the public’s takeaway from Mueller’s appearance when they go home to their districts is “OK, nothing new here,” Dewey said, lawmakers could find dwindling inspiration to push toward impeachment.Mueller’s ‘Flaws’Democrats are whiffing badly in their Trump investigations, said Representative Mark Meadows of North Carolina, and Mueller isn’t likely to help them. He said Republicans are prepared to cross-examine him on the “flaws” in his report. The Republicans back Trump’s assertions that the Russia probe was tainted by anti-Trump bias and government “spying” from the beginning.“For two years they claimed collusion -- strike one. For months they have twisted a no-indictment report into an obstruction case of a crime that didn’t exist -- strike two,” Meadows said. “Now they believe a TV hearing will help them recover from hype that has left so many underwhelmed. It will be strike three with no batters on deck.”After winning control of the House in the November midterm elections, Democrats entered this year holding the gavels of the six key investigative committees. They promised to use their subpoena powers to make alleged abuses by Trump their top oversight priority. They hit the administration with a dragnet of demands, vowing to obtain Trump’s tax returns and other material, and all relevant testimony.But with the prospect of an impeachment inquiry put off to the side by Pelosi, there’s been no master plan and no end game. Democrats have pursued scattered issues, from the administration’s bid to add a citizenship question to the U.S. Census to allegations that Kellyanne Conway, the president’s counselor, violated the Hatch Act by issuing partisan broadsides on the public payroll.The Committee on Oversight and Reform last month did find Attorney General William Barr and Commerce Secretary Wilbur Ross in civil contempt of Congress in the census dispute. But Democrats have yet to go to court to follow through on that case.Neither have they done so on the administration’s broad assertion of executive privilege to prevent testimony by officials such as former White House Counsel Don McGahn, who was a key source for Mueller’s account of potential obstruction by Trump.Such cases could become mired in the courts for months or years once they are filed.Oversight Chairman Elijah Cummings of Maryland said the fights with the president and the Justice Department over witness appearances and the refusal to turn over other information has been "making it almost impossible for the committees to do their jobs."On Monday, Cummings wrote the White House to complain of its “complete refusal to produce a single document” for the committee’s investigation of the use of personal email by officials including the president’s daughter Ivanka Trump and her husband Jared Kushner -- an inquiry begun when Republicans controlled the committee.With Mueller testifying shortly before Congress takes its summer recess and with election year approaching, some Democrats say there would be little time left to open an impeachment inquiry even if the hearings provide new momentum.“I think if we did an impeachment inquiry, you’d have to start by September,” said Budget Committee Chairman John Yarmuth of Kentucky. “You don’t want to start it when the primaries are going on."(Updates with Trump tweet in fifth paragraph.)To contact the reporter on this story: Billy House in Washington at bhouse5@bloomberg.netTo contact the editors responsible for this story: Michael Shepard at mshepard7@bloomberg.net, Larry Liebert, Bill FariesFor more articles like this, please visit us at bloomberg.com©2019 Bloomberg L.P.