Former FBI Director James Comey's dramatic testimony drew invective from his former boss, US President Donald Trump, on Twitter, with Trump dismissing him as a leaker on Friday (June 9) and a coward on Sunday (June 11)."I believe the James Comey leaks will be far more prevalent than anyone ever thought possible. Totally illegal? Very 'cowardly!'" Trump tweeted on Sunday.The president denied trying to interfere with the investigation and said he would be willing to testify under oath about his interactions with Comey.The president's tendency to bring up the Russia investigation, whether by insulting Comey or suggesting the existence of tapes, has created a headache for members of his party who want to put Republican priorities, including healthcare and tax reform, front and center.