Story highlights Flynn retired in the face of mounting controversy

Here are some of his potential replacements

Washington (CNN) Michael Flynn tendered his resignation as national security adviser on Monday night, creating an opening in one of the most important positions in the White House.

President Donald Trump tapped retired Lt. Gen. Keith Kellogg to serve as acting national security adviser, elevating the man who served as the national security council's chief of staff to the top role on a temporary basis.

Kellogg is in the running to hold the position full-time, as well as retired Gen. David Petraeus and former Vice Admiral Bob Harward, a source told CNN Monday evening.

But Harward is considered the top contender for the job, a senior official told CNN Tuesday.

Harward

Then-Navy Vice Admiral Robert S. Harward (right) attends the "Eager Lion" joint military exercise at the King Abdullah Special Operations Training Centre in Amman on May 27, 2012.