U.S. President Donald Trump’s attorney says his legal team would go to court to prevent any effort to subpoena the president.

Rudy Giuliani appeared on ABC’s “This Week” on Sunday, a day after it was revealed that Trump’s lawyers wrote a secret 20-page letter to special counsel Robert Mueller arguing that the president can’t be compelled to testify in front of a grand jury.

Giuliani says they would contest it if Mueller tried.But the former New York City mayor suggested that he did not entirely agree with the letter’s premise that a president could never be charged with obstruction of justice.

Later on Sunday Trump tweeted that the FBI should have informed him so that he would not have hired his former campaign manager Paul Manafort, who is currenlty under indictment by the special counsel for conspiracy, money laundering, financial, and making false statements charges - among others.

Trump wrote: "As only one of two people left who could become President, why wouldn’t the FBI or Department of “Justice” have told me that they were secretly investigating Paul Manafort (on charges that were 10 years old and had been previously dropped) during my campaign? Should have told me!

....Paul Manafort came into the campaign very late and was with us for a short period of time (he represented Ronald Reagan, Bob Dole & many others over the years), but we should have been told that Comey and the boys were doing a number on him, and he wouldn’t have been hired!"