Madam President and Her Dragon Bodyguard by Terri A. Wilson

As the President of the United States, Angela Bishop protects every American. But who protects her?

Blake Sullivan is the youngest son of the oldest dragon clan in North America. He was his father’s favorite until his mate’s murder sent him into a tailspin that ended with him wandering the world. Alone. Which was just how he wanted it.
Angela Bishop never wanted to be in politics. After her husband died, she was approached with an offer she couldn’t refuse. She never dreamed that offer would lead to the White House. Today, as the first female president, she brings a unique spin on world politics, but not everyone appreciates it.
Now, when a wizard sets his sights on world domination combining his magic with nanotechnology, Blake has to harness his anger and protect Angela, even though, she’s the one person who could destroy all dragons.