Joseph Maguire, acting director of national intelligence, speaks during a House Intelligence Committee hearing in Washington, D.C., on Thursday, Sept. 26, 2019.Andrew Harrer | Bloomberg | Getty ImagesThe House Intelligence Committee’s top Republican told acting intelligence chief Joseph Maguire to “be careful what you say” in his public hearing Thursday.Rep. Devin Nunes, the committee’s ranking member and one of President Donald Trump’s most loyal allies in Congress, told Maguire that “we appreciate you being here and have fun” — but warned him to watch his words because the panel’s Democrats are “going to use these words against you.”Maguire, who was appointed acting director of national intelligence in early August, responded: “Either way, I’m honored to be here and I’m honored to be leading the intelligence community.”A spokesman for Nunes did not immediately respond to CNBC’s request for comment.Maguire’s testimony began less than two hours after the public release of a whistleblower’s complaint about Trump’s call with Ukraine president Volodymyr Zelensky in late July. Media reports about that call, in which Trump asks Zelensky “if you can look into” issues related to former Vice President Joe Biden and his son Hunter, led Democratic leaders to announce a formal impeachment inquiry into Trump earlier this week.The complaint details an “urgent concern” that Trump is “using the power of his office to solicit interference from a foreign country in the 2020 U.S. election.”The whistleblower did not hear the July 25 call firsthand but cites accounts from more than half a dozen U.S. officials. It also alleges administration efforts to “lock down” records of the conversation, identifies Trump’s personal lawyer, Rudy Giuliani, as a “central figure,” and says Attorney General William Barr “appears to be involved as well.”White House press secretary Stephanie Grisham said that complaint “shows nothing improper.”But Intelligence Committee Chairman Adam Schiff, D-Calif., characterized Trump’s call with Zelensky—in which the president asks for “a favor”—as a “classic organized-crime shakedown.”Schiff questioned Maguire’s decision to refer the complaint — which contained allegations against Trump and Barr — to the White House and to the Department of Justice’s Office of Legal Counsel, rather than handing it over to Congress, which Democrats say is required by law.Maguire said he “thought it would be prudent” to ensure that there were no conflicts regarding executive privilege.”I believe everything in this matter is totally unprecedented,” Maguire added when his decision to delay sending the complaint to Congress was questioned.Nunes called the Democrats’ allegations against Trump the “latest information warfare operation against the president,” following the end of former special counsel Robert Mueller’s probe of Russian election meddling, possible Trump campaign coordination with Russia and possible obstruction of justice by Trump. Nunes temporarily recused himself from his committee’s own Russia investigation, following allegations that he may have shared classified information.This is developing news. Please check back for updates.