Here are 5 possible replacements for Michael Flynn as national security adviser

Former National Security Adviser Michael Flynn's abrupt resignation made waves on Monday evening, as pressure mounted amid controversy over his communications with a Russian ambassador.

Nevertheless, as the principal adviser on national security issues, the opening in President Donald Trump's administration is a crucial one that the administration is most likely to fill quickly.

Vice Adm. Robert Harward, a former deputy commander of US Central Command, is the front-runner to replace Flynn, according to Washington Post reporter Robert Costa. The New York Times also reports that Harward is the leading candidate to take over.

The position is appointed by the president, and does not require a lengthy confirmation hearing from the Senate.

Here are five possible candidates that may become the next national security adviser to Trump:

Peter Jacobs contributed to this report.

Retired Gen. David Petraeus

Retired Gen. David Petraeus' career includes 37 years of service in the US Army and a role as Director of the Central Intelligence Agency.

Stephen J. Hadley

Stephen Hadley served as the National Security Adviser to President George W. Bush from 2005 to 2009.

He served on several advisory boards, including defense firm Raytheon, and RAND's Center for Middle East Public Policy. Together with former Secretary of State Condoleezza Rice and former Secretary of Defense Robert Gates, he helps head the international strategic consulting firm, RiceHadleyGates LLC.

He also wrote the "The Role and Importance of the National Security Advisor," which, as the title implies, is an in-depth study of the National Security Adviser's role.

Retired Gen. Keith Kellogg

As the interim National Security Adviser filling in for Michael Flynn, retired Lt. Keith Kellogg was

and was part of computer software giant Oracle's h

Tom Bossert

Deputy Homeland Security AdviserGeorge W. Bush

Retired Vice Adm. Robert S. Harward

Retired Vice Adm. Robert S. Harward is a US Navy SEAL and the former Deputy Commander of US Central Command (CENTCOM).

He served as the commander of SEAL Team 3 and was the Deputy Commanding General of Joint Special Operations Command (JSOC). Harward also served on the National Security Council as the Director of Strategy and Policy for the Office of Combating Terrorism, and is also the CEO for Lockheed Martin in the United Arab Emirates.

Here are 5 possible replacements for Michael Flynn as national security adviser

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