You've got three weeks to get this backslider back into fighting trim.
From the time.com
More hawkish contenders, such as his foreign minister, Avigdor Lieberman, might have painted him as a backslider-and defeated him.
From the economist.com
Christianity is the big backslider.
From the economist.com
Petunia's faith has redeemed husband and wife, but there's a playful hint that Joe, an incorrigible backslider on Earth, might not place complete trust in what awaits him at the summit.
From the washingtontimes.com
More examples
Recidivist: someone who lapses into previous undesirable patterns of behavior
Backsliding is a term used within Christianity to describe a process by which an individual who has converted to Christianity reverts to pre-conversion habits and/or lapses or falls into sin. ...
The Backsliders are a three piece Australian band; self described as playing "Delta-blues wall of sound". The current line up (as of Dec. 2007) consists of Guitarist/Vocalist Dom Turner and drummer/percusionist Rob Hirst joined non alternating nights by either Brod Smith or Ian Collard on harmonica.
(The Backsliders (Texas band)) The Backsliders (often capitalised as THe BAcksliders) is a rock and roll band from Dallas, Texas.
A recidivist; one who backslides, especially in a religious sense; an apostate