WASHINGTON — A growing campaign by President Trump’s most ardent supporters to discredit the special counsel, Robert S. Mueller III, and the law enforcement agencies assisting his investigation is opening new fissures in the Republican Party.
Some lawmakers are questioning the damage being done to federal law enforcement and to a political party that has long championed law and order.
A small but vocal group of conservative lawmakers, much of the conservative media, and, at times, the president himself have launched a series of attacks to paint not only Mueller but institutions once considered sacrosanct to Republicans such as the FBI and Department of Justice as dangerously biased against Trump.
One of them, Representative Francis Rooney, a Florida Republican, called Tuesday for top FBI and Justice Department officials to be “purged.”
Now some Republican lawmakers are speaking out, worried that Trump loyalists, hoping for short-term gain, could wind up staining the party, dampening morale at the FBI and Justice Department, and potentially recasting Democrats as the true friends of law enforcement for years to come.
Straddling both camps is Trump, who in an interview Thursday with The New York Times lavished praise on Republican congressmen who have defended him from a “witch hunt” and expressed confidence that Mueller would “treat me fairly.”
The effort to sow doubt about Mueller’s team and the department that appointed him has gained steam since early December after Michael T. Flynn, Trump’s former national security adviser, pleaded guilty to lying to the FBI and cut a deal to cooperate with Mueller’s inquiry.
The following day, The Times reported that Mueller had removed a top FBI agent during the summer over text messages expressing anti-Trump political views that he had exchanged with an agency lawyer.
The news — and the Justice Department’s release days later of many of the text messages — provided Republicans ammunition of a sort they had long lacked: senior officials involved in both the investigation of the Trump campaign and of Hillary Clinton’s use of a private e-mail server railing against the president in private.
Since then, Republicans who control key House committees have called top Justice and FBI officials to Capitol Hill for hourslong interviews in public and behind closed doors about the handling of the Clinton and Trump investigations.
They have accused one of Mueller’s top deputies of anti-Trump bias based on an e-mail sent in early 2017 praising the acting attorney general for her decision not to defend Trump’s first travel ban in court.
And they have pointed to the actions of another senior Justice Department official, Bruce Ohr, as a predicate for the appointment of a second special counsel to investigate political partisanship in the department’s handling of the Trump-Russia investigation and its decision not to charge Clinton in the e-mail case.
“The public trust in this whole thing is gone,” Representative Jim Jordan, an Ohio Republican who has helped lead the charge, said during a tense Dec. 13 hearing with Deputy Attorney General Rod J. Rosenstein.
Trump himself has alternated between playing coach and cheerleader, repeatedly painting the Mueller and congressional investigations as partisan attacks and top FBI officials as Clinton loyalists. In the Thursday interview, he said Mueller’s investigation made the country “look very bad.”
He asserted 16 times that Mueller’s inquiry would discover “no collusion” with the Russians but suggested there was evidence the Democrats had teamed up with Russia to produce a dossier of opposition research on his campaign’s contacts with Russia.
And while Trump’s lawyers have maintained a cooperative posture with Mueller and investigators on Capitol Hill, he lavished praise on the Republican House members who have led the attacks on investigators.
“Great congressmen, in particular, some of the congressmen have been unbelievable in pointing out what a witch hunt the whole thing is,” Trump said.
To some Republicans, the attacks have gone too far and are not representative of rank-and-file Republicans in Congress.
“Most of my Republican colleagues feel as I do that we have confidence in law enforcement,” said Representative Charlie Dent, a moderate Pennsylvania Republican. “I don’t know why that should change now that we have a Republican administration.”
Senate Republicans, with few notable exceptions, have put forward much more muted criticisms of Mueller, centered mostly around his choice of deputies — several of whom have made donations to Democratic political candidates. Senators have largely avoided criticizing law enforcement agencies outright.