Telegraph - His administration dealt a significant blow after not even a month in office, President Donald Trump must now fill a vital national security post after the resignation of embattled national security adviser Michael Flynn.
Mr Flynn stepped down late on Monday, ending days of speculation about his fate following reports that he had misled Vice President Mike Pence and other officials about his contacts with Russia.
Mr Flynn conceded that discussions of sanctions may have come up during several calls with the Russian ambassador during the transition period leading up to Mr Trump's January 20 inauguration.
He acknowledged he gave "incomplete information" about those discussions to Mr Pence who, apparently relying on information from the national security adviser, initially said Mr Flynn had not discussed sanctions with the Russian envoy
Mr Trump named retired Lt. Gen. Keith Kellogg as the acting national security adviser and a senior administration official said he was one of three candidates the president was considering to replace Mr Flynn on a permanent basis.
Whoever emerges as Mr Trump's choice will take the helm of the National Security Council at a time when the young administration is grappling with a series of national security challenges, including North Korea's reported ballistic missile launch. The president, who was joined at his Mar-a-Lago estate by Japanese Prime Minister Shinzo Abe over the weekend, voiced solidarity with Japan.
Here's a look at the top named contenders for the post, which does not require Senate confirmation:
Retired Lt Gen Keith Kellogg
Mr Kellogg had previously been appointed the National Security Council chief of staff and, along with Mr Flynn, advised Mr Trump on national security and foreign policy issues during the campaign. He had been considered for national security adviser before the post went to Mr Flynn.
The 72-year-old is a decorated Army veteran who served two tours in Vietnam War, where he earned a number of medals, including the Silver Star. He served as the commander of the famous 82nd Airborne Division from 1997 to 1998.
Mr Kellogg was chief operating officer of the Coalition Provisional Authority in Iraq, the interim governing body following the fall of Saddam Hussein in 2003.
He previously worked as executive vice president of research and technology for Virginia-based information technology firm CACI International, which works as a contractor for defence, intelligence and homeland security agencies.
The most audacious choice would likely be former CIA director David Petraeus. General Petraeus, a retired four star general, was bounced from his position atop the intelligence agency in 2012 after he it was revealed that he passed on classified information to his biographer, who had also become his mistress.
But Mr Trump during the campaign spoke sympathetically about General Petraeus' plight despite his frequent criticisms of his Democratic opponent Hillary Clinton for mishandling classified materials.
Mr Petraeus was briefly under consideration to become secretary of State before Mr Trump picked Exxon CEO Rex Tillerson.
He was also reportedly under consideration for the post of defence secretary. Asked at the time if he would agree to serve in the Trump administration, General Petraeus said: "I've been in a position before where a president has turned to me in the Oval Office in a difficult moment and .... said 'I'm asking you as your president and commander-in-chief to take command of the International Security Assistance Force in Afghanistan'.
"The only response can be 'yes, Mr President'."
Pressed further on whether he had confidence that Mr Trump was capable of serving as president, General Petraeus said: "I think so, yes. It's up to Americans not only to hope that that is the case, but if they can, endeavour to help him."
Retired Vice Admiral Robert Harward
Robert Harward, a Navy Seal, served as Deputy Commander of the United States Central Command when it was under the command of General James Mattis, who is now secretary of Defence.
He served on the National Security Council for President George W. Bush and commissioned the National Counter Terrorism Centre.
NEW: Vice Adm Robert Harward is top choice to replace Flynn, per WH sources. pic.twitter.com/7E1XPwa60X
— Peter Alexander (@PeterAlexander) February 14, 2017
Upon retirement in 2013 after a nearly 40-year career in the Navy, Harward took a post as a chief executive officer for defence and aerospace giant Lockheed Martin in the United Arab Emirates.
Mr Trump has recently been in very public negotiations with Lockheed over the cost of its F-35 fighter jet programme.
Numerous reports have placed Mr Harward as the early frontrunner for the job.