Jake Sullivan (Photo by Matt McClain/The Washington Post via Getty Images)WILMINGTON, Del. - President-elect Joe Biden appointed Jake Sullivan as his national security adviser Tuesday.Sullivan, 43, will be one of the youngest people to serve in that role.Biden introduced Sullivan in Wilmington, Delaware along with other nominees for his foreign policy and national security teams.RELATED: Biden picks Blinken, Mayorkas, Sullivan for key Cabinet positionsPresident-elect Joe Biden introduced key members of his foreign policy and national security team Tuesday.Sullivan briefly took to the podium, thanking Biden for the honor. “I pledge to you and to the American people that I will work relentlessly in service of the mission you have given us,”.