Biden tops list of potential 2020 Democrats in new poll
Rubio lands another lawmaker endorsement
In a statement first obtained by The Hill, Mullin lauded Rubio's "strong understanding" of foreign policy and argued that he's best equipped to keep the nation safe from the threat of terror groups.
"I have always been clear that the person I will support for president must be a true leader - someone who can unite our country and move our nation forward," Mullin said. "I believe Marco Rubio is that person."
"One of the most important jobs of our next president will be keeping this country safe," he continued. "Senator Rubio has the knowledge and understanding of the serious threats facing this country."
Rubio also landed endorsements this week from Reps. Mia Love (R-Utah) and Doug LaMalfa (R-Calif.), both of whom cited his strength on national defense as reasons for supporting him.
Jeb Bush still boasts the most supporters on Capitol Hill but Rubio is inching closer to him.
Bush has the support of 25 members of the House and three U.S. senators, according to the FiveThirtyEight endorsements tracker.
Rubio is in second place in the endorsements primary, and now counts 13 House members and three senators in his corner.
However, most of Bush's endorsements came early in the cycle, while Rubio has doubled his lawmaker support over the last few weeks.