Donald Trump insisted he has the "legal right" to intervene in criminal cases on Friday, a day after his attorney general William Barr publicly rebuked the president, saying his tweets were making it "impossible" for him to do his job. Ignoring that request, Mr Trump quoted Mr Barr"s comments that the president “has never asked me to do anything in a criminal case” in another tweet. But Mr Trump went on to say: “This doesn’t mean that I do not have, as President, the legal right to do so”. The comments broke with a tradition observed by presidents since the Watergate scandal to allow the Justice Department to carry out investigations free from political influence. On Thursday night Mr Barr, the US attorney general, delivered a rare public critique of Mr Trump amid a growing controversy over the president"s involvement in the sentencing of his longtime friend and former political adviser Roger Stone. “To have public statements and tweets made about the [Justice] department... about cases pending in the department and about judges before whom we have cases make it impossible for me to do my job," Mr Barr told ABC News. Earlier in the week prosecutors had recommended Stone face seven to nine years in prison for his obstruction of justice, lying to Congress and witness tampering convictions. Mr Trump tweeted that this was a "miscarriage of justice" and shortly afterwards the Justice Department"s leadership overruled its own prosecutors to request a less severe sentence. All four prosecutors quit the case in protest. In his ABC interview, Mr Barr claimed he had already begun amending the Stone sentencing recommendation when he became aware of the president"s tweets. "I don"t pay attention to tweets and I"m going to pay attention to directions and do something I think is wrong," Mr Barr said, in a rare public criticism by a sitting cabinet member. Asked whether Mr Trump was within his rights to direct Mr Barr to ask for an investigation, the attorney general said it would "perfectly appropriate" in many areas such as in a terrorism or bank fraud case. "If he were to say "go investigate somebody because" and you sense that it"s because they are a political opponent then an attorney general shouldn"t carry that out - wouldn"t carry that out," he added. Mr Trump was recently acquitted of impeachment articles over a request to the Ukrainian government for an investigation into a political opponent. A whistleblower complaint which triggered the impeachment proceedings alleged Mr Barr was involved in the effort, a claim the attorney general denied. Mr Barr has previously been attacked for his involvement in a string of politically sensitive cases which opponents say have defended Mr Trump"s interests. The most contentious of these was Mr Barr"s summary of a report into potential collusion between the Trump campaign and Russia, in which he failed to describe Mr Trump"s attempts to obstruct the investigation outlined in the report. Mr Barr has also reportedly assigned an outside prosecutor to re-examine the case against another of Mr Trump"s former advisers, Michael Flynn, who is awaiting sentencing after admitting lying to the FBI over his contacts with the Russian ambassador to Washington. According to the New York Times, Mr Barr has also brought in outside prosecutors to re-examine the handling of other politically sensitive national security cases. The unusual move will heighten the controversy surrounding Mr Barr who is facing accusations of interfering with the work of career prosecutors. Nancy Pelosi, the Democrat House Speaker, criticised Mr Barr on Thursday, calling him one of Mr Trump"s "henchmen." "The attorney general has stooped to such levels," Mrs Pelosi said. "What a sad disappointment. The American people deserve better."