Top US officials opened a secret obstruction of justice probe into Donald Trump after he sacked FBI Director James Comey, it has been revealed. Deputy Attorney General Rod Rosenstein and then-acting FBI Director Andrew McCabe became increasingly troubled by Trump’s behaviour following the firing. In an attempt to reign him in, the Department of Justice launched an obstruction of justice investigation into the president’s potentially unconstitutional operations. The covert scheme was actioned after officials grew increasingly more worried about Trump’s attempts to control other government operations – particularly Comey’s investigation into his former security advisor, Michael Flynn, CNN have said . Trump’s personal lawyer, Rudy Giuliani, said on Thursday that Trump had a ‘legal right’ to fire Comey. “It’s shocking that the FBI would open up an obstruction case for the president exercising his authority under Article II,” Giuliani told CNN. The investigation started in the eight days between Comey’s termination and special counsel Robert Mueller’s appointment. Rosenstein appointed Mueller on May 17, 2017, to lead the now-19-month-long deep dive into investigating alleged collusion between the Trump administration and the Russian government. Last year, the Washington Post reported that the DOJ had commenced its own research project into Trump. As part of the discussions about how to rein in Trump, Rosenstein had offered to wear a wire while meeting with Trump, though he has later said he was joking. He also reportedly proposed looking into whether Cabinet members would be willing to impeach Trump using the 25th Amendment.