U.S president Donald Trump announced Kelly would replace his embattled chief of staff Reince Priebus at the end of a particularly chaotic week that saw his first legislative effort - healthcare reform - fail in Congress.

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While speaking at the white house Trump said, " we just swore in General Kelly, He will do a spectacular job, I have no doubt as chief of staff".

Retired Gen. John Kelly, previously the Homeland Security secretary, took over on Monday from the ousted Reince Priebus. Trump hopes Kelly can bring some military order to an administration weighed down by a stalled legislative agenda, a cabal of infighting West Wing aides and a stack of investigations.

Still, Kelly's success in a chaotic White House will depend on how much authority he is granted and whether Trump's dueling aides will put aside their rivalries to work together. Also unclear is whether a new chief of staff will have any influence over the president's social media histrionics.

Former Trump campaign manager Cory Lewandowski, who was ousted from the campaign in June 2016, said on NBC's "Meet the Press" that he expected Kelly would "restore order to the staff" but also stressed that Trump was unlikely to change his style.

"I say you have to let Trump be Trump. That is what has made him successful over the last 30 years. That is what the American people voted for," Lewandowski said. "And anybody who thinks they're going to change Donald Trump doesn't know Donald Trump."

Kelly's start follows a tumultuous week, marked by a profane tirade from the new communications director, Trump's continued attacks on his attorney general and the failed effort by Senate Republicans to overhaul the nation's health care law.

In addition to strain in the West Wing and with Congress, Kelly starts his new job as tensions escalate with North Korea. The United States flew two supersonic bombers over the Korean Peninsula on Sunday in a show of force against North Korea, following the country's latest intercontinental ballistic missile test. The U.S. also said it conducted a successful test of a missile defense system located in Alaska.