WASHINGTON/NEW YORK (Reuters) - President Donald Trump brushed off the first indictments in the probe of his campaign’s ties to Russian election meddling, but the charges sent a clear signal to the White House and other Trump associates: Robert Mueller means business. By going after Trump’s campaign manager and another aide on money-laundering charges and securing a guilty plea from a third campaign adviser, the special prosecutor showed he would delve deeply into the past in search of criminal activity and use his broad powers aggressively. That left some Trump associates worried about what or whom Mueller would target next, despite the White House’s public dismissal of the developments as unrelated to the president and his campaign. “They’re flexing their muscles for anybody that they approach in this investigation and letting them know we really mean it,” said former federal prosecutor Patrick Cotter. “So if we come to you, you should talk to us. Manafort didn’t and look what happened to him.” Manafort and Rick Gates are charged with money laundering, tax fraud, conspiracy to defraud the United States, and other counts. They pleaded not guilty on Monday. The indictments, which closely detail the alleged crimes, appeared to be an opening salvo from Mueller. He was appointed by U.S. Deputy Attorney General Rod Rosenstein in May after Trump fired FBI Director James Comey, who had led an investigation into whether the Trump campaign colluded with Russia to influence the 2016 election. Mueller was given a mandate to probe potential collusion and “any matters that arose or may arise directly from the investigation.” Trump has denied any collusion with Russia and at times described the investigation as a “hoax” and a “witch hunt.”     Russia has denied interfering with the 2016 election. With the first indictments on Monday, Mueller showed he was not afraid to use his powers, and Trump officials noticed. “One thing I’m worried about in a bigger scale is that Rosenstein, by giving Mueller this wide berth, has created this monster,” said one former White House official, who spoke on condition of anonymity.  A former Trump campaign adviser fretted that the probe could, as a result, touch on Trump’s businesses, too.  In a New York Times interview in July, Trump indicated that Mueller would be crossing a red line if he investigated Trump’s family business.     Legal experts said Mueller would not be swayed by Trump’s view of the proper scope of the investigation. “I don’t think prosecutors concern themselves with what politicians say about red lines being drawn,” said former federal prosecutor Robert Capers. Jens David Ohlin, a professor of criminal law at Cornell Law School, said Mueller could be targeting alleged financial crimes by Manafort and Gates to gain their cooperation and uncover wrongdoing elsewhere. A number of lawyers said the guilty plea of George Papadopoulos, announced by Mueller’s team on Monday, could ultimately provide a closer link to the campaign and pressure others to open up. While the charges against Manafort and Gates were not related to their campaign work, Papadopoulos admitted he lied to the Federal Bureau of Investigation about his contacts with foreign nationals he believed to be tied to the Russian government while he was a campaign adviser. Prosecutors said they arrested Papadopoulos in July and that he was cooperating with the government.  “God knows what this guy’s going to say now,” said the former Trump campaign adviser. “Since he’s cooperating, he could set any perjury traps up for others.” Cotter said Mueller’s unveiling of Papadopoulos’ guilty plea “was to head off any arguments that the case against Manafort and Gates is not about Russia.”  Frank Montoya, a former senior FBI agent, said Manafort’s indictment and Papadopoulos’ plea indicated Mueller was not going to bow to White House pressure and would keep pushing hard to uncover wrongdoing. “It is pretty much a road map – we are going to be looking at the money laundering, we are going to be looking at the failure to report income, we are going to be looking at the general criminal conspiracies. This is also about Trump’s red line – we are going to cross it. And we are going to keep looking at the so-called collusion, or the coordination with the Russians to undermine democracy,” Montoya said. 