"Top Down," "The Double" and "Blowback" are newly released
thrillers with a Washington theme. (Keri Wiginton, Chicago
Tribune)  Alan Cheuse looks at three new thrillers with a
Washington, D.C. theme that are worth checking out.  "Top Down"
by Jim Lehrer, Random House, 208 pages, $26  The devastating
work of an international shooter appears in Newshour veteran Jim
Lehrer's 22nd novel, "Top Down." His premise is that on the day
of John F. Kennedy's assassination, a Secret Service Agent named
Van Walters checked the Dallas weather and OKed the removal of
the bubble top from the presidential limo, thus inadvertently
giving Lee Harvey Oswald a clear shot. Five years later, a young
Texas journalist named Jack Gilmore, who was covering the
Kennedy visit to Dallas that fatal day, hears from Walters'
daughter Marti. The decision to take that top off has ruined her
father's life, she explains. Gilmore, smelling a good story,
offers his assistance in helping the former agent through his
trauma. The reporter follows the