Edge of Danger by Jack Higgins

The Reckoning/Connection/Daughter team of Blake Johnson, head of the White House's secret Basement operation, and former IRA terrorist Sean Dillon is reunited. A half-British, half-Arab family named the Rashids is furious at what it sees as personal attacks on its power and honor, and they hold the Americans responsible -- and accountable. To that end, they plot the assassination of the President of the United States. Johnson and Dillon are on the case, but whether they can stop it is open to question. And even if they do, the Rashids have other plans. Their motto is, "I always return", and that's exactly what they plan to do....