Blood Oath, by Christopher Farnsworth

Zach Barrows is an ambitious young White House staffer whose career takes an unexpected turn when he's partnered with Nathaniel Cade, a secret agent sworn to protect the President. But Cade is no ordinary civil servant. Bound by a special blood oath, he is a vampire. Cade battles nightmares before they can break into the daylight world of the American dream, enemies far stranger-and far more dangerous-than civilians have ever imagined.

Blood Oath by Christopher Farnsworth is the first in a series of novels featuring Nathaniel Cade-the President's vampire.

www.presidentsvampire.com
(From the YouTube description)